Damage to Car

I left my car at the Stanstead I love to park, which is the same company as I love to meet and greet, from the 16th November 2015 - 22 November 2015 and when I returned there was damage to my rear bumper. When I left my car no annotated diagram of my car was done that I had to sign which would be good practice just like they do with hire car companies. When I pointed out the damage to the company the supervisor took a picture of the damage and said he would investigate. I wrote an e-mail to customer services on my return home. It was three weeks before they said that the investigation had been completed and they denied all responsibility. They said that all their drivers do annotated diagrams of the cars so the damage couldn't possibly have been done by them. My reply to this is that if the driver damaged the car while moving it. He would hardly incriminate himself by doing a truthful annotated diagram. Unfortunately it is my word against theirs. What I would advise anybody reading this is that don't leave your car with a company where you have to hand over you keys. It is much better to pay a bit extra and park in a secure car park where you park the car and take the keys with you.