Avis is robbing customers from their deposit

Avis not fair when it comes to deposits refunds. I was given a toyota starlet with 37 liters fuel tank and tis is what happened: 1. I returned the vehicle with half of fuel but the charged me for full tank which is R920 and the wrote that they poured 36 liters which does not make sense if the vehicle was at half tank. 2. The charged the extended 2 days from my deposit R700 which does not make sense hence all the arrangement were made by my insurance, meaning the got money double from my insurance and my deposit. 3. It has been more than their promised 7 days without refund. 4 in total my R2500 has resulted in R 720 .which I dis not get as yet.