Thrifty Car Rental does as they please with your deposit

Earlier this year I rented a car from Thrifty Car Rental. They took 6 weeks to return my deposit. During this time they repeatedly **** that it had been refunded until eventually someone called and admitted they had lost the banking details. Last week I returned another rental to them. It was due back at 9pm on Wednesday. I tried unsuccessfully to call them to extend until Thursday morning. They have now deducted R750 extra for late return penalty (I don't dispute the extra day rental they charged as well) and require me to get them proof from Telkom that I tried to call. They didn't care about holding my deposit for 6 weeks but charge R750 for returning the car 12 hours late (even though they also charged for the extra day).

I have repeatedly asked the Customer Services Director (Bjorn) to call me, but he simply ignores my requests. He also refuses to take calls.