Required to pay for damage not caused.

Took a vehicle from King Shaka Intl on 10th Jan. It was late evening and raining. Nobody bothered to inspect the vehicle with me. On returning the vehicle on 11 Jan, I was accused of damaging the vehicle - there were two dents on the bonnet, which I did not cause. I was asked to fill in a affidavit which I did and was told that the video footage would be checked to see if indeed nobody inspected. I then had a further amount reserved on my card (without my permission) and when I enquired I was told it was for damages I caused and that their investigation was complete. I am now having to pay R4600 for damage I didn't cause. I always believed Avis to be trustworthy so I accepted that vehicle was in good condition when handed to me. Feeling very disappointed. I asked if they had checked their video footage and no response. Please be more diligent if you use Avis. Check and check again even if its dark and raining. To be safest, just don't use Avis!