The car backed up and hit my car on the side as I was waiting for a car to get out of the pump area where I was trying to park. This car was initially in front of this pump area and suddenly backed up. As I was seeing the car coming, I honked by there was nothing else I could do. When I talked to couple of ladies, the daughter told me right away that she wasn't driving but she was the one driving. The mother gave her driver's license and each of us called our insurance companies. A few days later, I contacted my insurance and then told me that they ackwnoledge that they were backing up and confirmed that it wasn't my fault. Then, I received a letter from the ladies insurance saying that I had to cover for the car damages because the accident was my fault. I don't know how to go about it.