Control over my money

I rented a car from AVIS from the 5th to the 6th of February from their East London airport branch. I was quoted R 643 for the 48 hours. Upon receiving the vehicle AVIS took R2000+ and put it in a holding account. THIS MEANS THEY HAVE TOTAL CONTROL OF THE FUNDS THEY HAVE TAKEN. This already makes me feel uncomfortable as I'm used to paying once I've returned a vehicle. Then they explained that i would have to phone AVIS to return my money into my account because their is a problem with their system and the FNB debit card. I also fail to see AVIS as a customer service orientated company by me having to chase outstanding funds?Anyways i didnt manage to see on statements where my money was or where it went. A couple of days later i get an sms saying that R1063 was reserved for AVIS car rental. This is R400 more than what I was meant to pay. That means me having to pick up the phone to query the bill. Apparently the extra R400 was used to fill up the vehicle. Funny thing is the vehicle was checked upon return and filled by me before returning the car at the airport filling station for R169.26. Another strange thing is I didn't do enough km to warrant R400 worth of petrol.