Charged for damage I did not cause

I hired a car on the 20th Dec to return it at a different branch (Secunda). On arrival there was damage that I overlooked whilst receiving the car, the minor damage was on the black plastic part of the grill. I signed an incident report that stated that was the only damage. I was not so worried about his since I had taken out a minor damage waiver. When I enquired about my deposit 2 weeks later, only then was the assessment done and it had extra damage that was not included in the report. The incident report retained by europacar had extra additions compared to the copy they gave me. The extra damage added included scratches on the bumper, dents on the passenger door and more chips. The total damage amounted to R 12000 including metallic paint work when the only damage caused was on plastic. Today my credit card was credited with an extra R 5800 with the other retained deposit. I called the branch and the agent who received the car confirmed that he received the car with only the grill damage. Why am I being charged for damage I did not cause.