Europcar took money for damages I didn't do

I hired a car to go to a wedding. When I received the car there was no one to do an inspection with me. We were handed a slip to sign and the consultant told us not to worry, it's not for damages it's just to show you we did the inspection. When I returned the car, I was immediately flagged to point out damage to the car. The damage is to the bumper on the underside. Impossible to see when walking around the car unless you get on your hands and knees to look. I have 4 witnesses including myself that can attest to the fact that I did not damage the car. They will have none of it. I immediately disputed the damage and they promised to investigate. I have spoken to the branch manager, the claims department and the claims manager. Not one of them ever got back to me. I had to continuously phone them. Each of them said they would investigate and not one of them ever phoned me back. The images on the damage report are also suspicious. They are unable to provide me an image of the damage including the license plate to prove the damage is to the same car. I must just take their word for it. I just feel as though I have been ******! The whole process was just a whitewash.