Another claim dispute

I collected a car at OR Tambo - no one checked the car with me, keys were given to me an off I went. I drove straight to Vanderbijlpark to deliver the car, only to be told there is a scratch on the back door which I will be held liable for. This could not have been caused by me, as I did not leave the car unattended at all. I was forced by the manager to write and sign an accident report. I used this service regularly for travel between Vanderbijlpark and OR Tambo, but I am so unhappy with this attitude that I will never use Europcar again. I am also afraid of what this about 5 cm scratch will cost me after reading all the other posts about Europcar. What happened to honest, straight forward service?