Avis unauthorized deduction from my bank account

Avis OR Tambo claimed that I have damaged the rental vehicle and instead of a R295 rate deducted R4500 from my bank account. They claim that I have scratched the car and the front bumper is dented. Where do I go to defend my case? There was no person to inspect the car when I returned it, the security guard told me to park it and leave the keys in the car. How do I defend my case?