Billed for a damaged that was already existing

Avis billed us for a dent that was always on the car but not visible since the cars are delivered to customers dirty. We were handed over a very filthy white vehicle and were told that they cant wash cars because of the water crisis in CPT, However now that there was a hidden dent which was later reveled when it rained prior to the vehicle drop off. We are no liable to this cost as we were not afforded the opportunity to inspect the car properly since it was dirty. this is ******* and we will never hire a car from Avis again!!!!! And we will not pay for a dent we didn't cause. Go try rob someone else.