DAMAGE DISPUTE / UNAUTHORIZED DEDUCTION OF FUNDS

I rented out a vehicle (RA: E***) from Avis Cape Town International on the 05th until the 09th of September. Upon collection of the vehicle at 22:20 I was assured by the teller agent (using a damage inspection sheet) that the vehicle was damage free. No physical inspection was conducted by a AVIS car inspector with me at that point as i was told they had knocked off. I also noticed nothing when i did a brief all round check before i drove off. I had no incidents with the vehicle throught the rental period. However, when i returned the vehicle, an inspection was done and a small dent was spotted on the driver side door. I told the inspector that this was a surprise to me and that it could've occured prior to my rental period as no inspection had been conducted when i took the vehicle. Also, given how small that dent was, i couldn't have noticed it at that time of the night. Now AVIS has deducted in excess of R5000 from my credit car for a damage that i know nothing about. I did not authorize this transaction but the customer service agent told me they would not be giving me back my money and that the damage claim will remain. I'm very disappointed with the service I've received and how this dispute was handled. I want my money back and i will not let up until that transaction has been reversed. I'm pursuing this matter legally and I've reported the transaction with my bank as well.