enterprise damage fraud claim mentor ohio

i rented a car for 2 days, the office was really busy and they were rushing me. They took the car and washed the outside when the girl came back she checked the gas gage and it was full and told me to bring it back with a full tank and to initial the paper contract. i walked around the car and didnt notice anything, it was a black car and also wet. i drove to a waterpark with no problems, knowingit was a rental car i parked far away, there were no cars by me at all, nobody nxt to me in front or behind. i drove the car straight back to enterprise the nxt day. a week later i received a letter from recovery services saying there was damage. i called and they did not care what i had to say. just that there was a dent on rear passenger door on the bottom, now im responsible to pay something i didnt do . i very upset and hurt, ill never feel comfortable renting a car again. please someone help me they should not be able to get away with this.