Why am I being asked to pay £100.... 6 months later ..

In April I had to take my family to a wedding in Birmingham, decided to rent a vehicle from enterprise who gave me cracking deal, I booked well in advance to ensure availabilty and recieved confirmation that all would be ok.. On the day I went to collect my vehicle there was about 4 cars still available that would have been accepatble for the catergory I had selected, which was a 2.0 litre care to seat 4/5 passengers.. was made to wait around for about 20 minutes then shown to a vehicle that I had not predicted was the one I was looking to hire, given the circumstance and time I accepted the vehicle, drove home and discovered that there was a number of faults with the vehicle and even the simplest fo things like the lighter plug did not work, therefore no chance of charging my phone or using my sat nav which was a must as I was travelling to areas that I am not that familiar with, so sat nav guidance a good friend. Took the vehicle straight back and asked if the could check the fuse box, this could not be done as there was no mechanical savvy people on hand so was offered a replacement. As all other cars had now been collected by others the only vehicle that was available was a Mondeo, which looked like it had driven through a field, they offered to clean the vehicle so I had to wait and was now running late for my journey.. first thing I noticed was the vehicle was parked up on a very high kerb and the NSF tire looked low in pressure, did question this but was told all was fine, car was given a quick wash and vac but no check was made of the tire or its pressure.. I did take out CDW on the vehicle and felt that this was a way fo them increasing the cost of rentals so your not getting it as cheap as you might think.. but not a problem I work in a corporate environment and this does seem to be the standard on all hire vehicles our organisation hires.
Was happy with the vehicle but after leaving the hire compamcy and getting home, loading vehicle with some luggage and family headed for fuel, at the station as I always do before any long journey do a basic check, the check proved my fears that there was something wrong with the NSF tire as it turned out be a lot lower in pressure than the other tires, so I topped this up and hoped it was just down to the way it had been parked and some alloy wheels can loose pressure around the seals if the tire is getting on a bit.. unfortunately this was not the case 90 miles into my journey it was starting to run flat so had to fill it again as I had no choice with the family in the car and I was quite close to Birmingham, could not locate the locking nut and even replacing the tire to the steal wheel would not be adequote due to the speed restriction with using one of these, managed to get to Handsworth and had to abandon the vehicle near a friends house and transport family with alternative means.. spoke to the recovery people as per number provided by enterprise was informed that they would send a recovery truck, I refused this as it was nothing they could do at this time of night and that I would want the tire repaired or replaced as I had a number of destinations to visit over the next 2 days and replacement of the wheel with steal wheel would not be sufficient. Agreed that they should arrange to contact me n the morning at 9am and we could then attempt to get it resolved as I was informed that they had a contract with local tire firms so would not be a problem, I did ensure that the vehicle was parked in a safe enough location under a street lamp and that it had been locked.. questioned if I would be charged and was advised that this was part of the service and there was no charge whatsoever.. felt assured and confident that I had asked all the relevent questions and also confident with the outcome as the call centre person seemed to know what they where doing and didnt seem to take long to sort everything out for the morning. Anyway got a call the next morning as promised from the AA who advised that he was around the corner from where I had advised the vehicle was parked and if I could meet him there, (note, I have now given up my sleep and additional time) I informed him of the exact location and said that i would be there within the hour as I was staying in another part of the city.. so put me skates on, got myself there and he had already jacked the vehicle up and and had examined the wheel, his theory was, there is a screw in the centre of the tire and the head of the screw had sheared off thus being the reason the tire had gone flat, asked when this could have happened, he said, not sure, could have been in there for weeks or days as it wore completely out before causing the tire to go flat, asked if it could be repaired as the tire looked in fair condition, he replied yes but hire companies tend to replace tires rather than repair, asked would I have to pay, he said this should be covered, asked can you check and so he did, first he completed a temporary repair by filling with some paste.. then he called and confirmed that there was no charge and that this was fully covered so I should have to apy anything towards it.. fine,, followed AA to National Tires and Autocare at Hockley flyover in birmingham.. AA spoke to the staff there and was told to wait in the reception area whilst they took a look and carried out the repair, asked the tire man, who pays, he said its on contarct once they provide a confirmation reference will replace tire, I said why not fix its completely rapairable, he said we dont, AA put paste in there, dont want to clean it out and enterprise will just want it replaced.. said ok.. do I pay.. said no.. all covered.. dealt with very efficiently and politely and the repair was carried out within the hour, left happy with the service recieved but dissapointed that I had been given a vehicle that clearly had this fault and had to waist my morning resolving an issue that should not have really occured. Anyway that was Saturday morning, arrived back in Cardiff on Monday and returned the vehicle, had a legthy conversation with the chaps at enterprise on ipswich rd depot and explained the story probably in more deatil than I have done here.. LOL.. was told that I had taken the additional insurance cover CDW and that everything was covered and that I would not be charged, the £250 deposit was transferred back to my bank account and was given an apology for the inconvenience.. apart form the hassle I went through on the friday with the vehicle change and then the flat tire, felt that I had been dealt with professionally and confident that had been told the truth.. anyway.. that was April, its now December and I being chased for £100 for a tire.. not sure why, I asked this question more than 3 times from all parties so why have they now decided that I am liable, I am confident that the tire was faulty from the start and just glad it did not blow out with my family in the car on the M5..I asked them to check it and they didnit, as I watched them clean it and vac it only.. I refuse to pay this at such a late time, if they had raised this at the time maybe we could dealt with it on the spot, also the hassle I had to go through to get it fixed is worth more than that, I got some company called Regal asking me to contact them. not sure what to do, I have attempted to contact them today but got a message saying please text this number which I have.. I will be refusing to pay so will see what happens..
Mr A Khan