No refund!! money missing!!!!

Myself and my boyfriend went to Cape Town from the 2nd of March to the 12th. During that period we used Tempest Car Hire , When we arrived to fetch the car, there was a payment of R6497.90 that was paid on the spot. We were told that once the car is returned, the deposit would be paid back in full. The car was clean and had a full tank. When we returned the car, we had filled the tank and cleaned the car. There was a refund of R1008.90 returned? how is this calculated out of R6497.90 ? when i called and asked for a itemized billing, it was promised to be sent within the hour? a week later, i called again and same response. I phoned again the following week to finally be helped by someone. Once i received the itemized billing which was completely different to the first one i received when collecting the car. When i phoned to ask them to explain to me how all of a sudden R4000 + has just vanished, i was put on hold and the call was ended!! Every time i bring up my complaint, the call gets either put on hold for ages or the call is dropped!!!