Avis Falsely blaming customer for a small scratch on bottom of front bumper

I am extremely disappointed by Avis (Sandton). They took over R11000 from my account inclusive of the deposit & the rental amount. I returned their vehicle yesterday 2020/10/12 intact, washed & clean. The car already had a small scratch on the bottom corner of the front bumper the assessor "Nenzhelele" checked the vehicle the first time around & said all is well, then about 5 minutes later he comes into the office where my refund was supposed to be processed & tells me there is a small scratch on the bumper, the scratch was already there from when I initially collected the vehicle & now Avis is blaming me for the scratch and withholding the funds that they took from my account. I would not recommend their service.