What a rip off!!!

We hired a car from Hertz and paid in advance. We collected the car as arranged from Knock Airport in Ireland on 25th October and returned it on 28th October. The petrol tank was full on collection and we were warned that it needed to be full on return. We are used to this requirement having used car rental on numerous occasions. We only used the car for the journey to and from the airport and for a very short drive, a total of less that 60 miles as we were staying with family and driven in their car during our stay. We filled up the car on our way back to the airport and it took 15euros of fuel. My credit card bill today shows that I have been charged £76.53 for fuel. As I do not have a receipt for the fuel I cannot confirm that the tank was full and so Hertz are having to enter into dispute with the airport. If they do sort this out quickly and refund my money, I will be happy to update the fact on this site. If not.....please learn from my experience.