AVIS robbing their customers!!! They won't return your deposits. Stay away

I collected a rental car on the 10th of April. I then returned the card on the 22 of April with a full tank of petrol. On collection I was charged R2500 and was advised that it would be returned to my account on return, minus the missing petrol and tollgates. I have still not received a refund or reason of any sort, for not receiving my money back. I have reached out to their call center, I have tried escalating the situation, with no success. Initially I had to wait 7-20 business days for the refund. After escalation I needed to wait 5-7 business days. FYI 31 business days has passed. Wonder what would happen if we did the same - Fetch the car and advise AVIS that we would pay in 7-20 business days. Guessing that would not go so well. So why are you treating customers like this.