Thrifty Refuses to Pay Rental Vehicle Deposit after return of Vehicle

I booked a vehicle from Thrifty from 30 September - 1 October. When booking the vehicle I was made to pay a R4000 deposit, while I duly paid. I was then told my money would be paid back to within 7 days. It is almost the end of October now and I have still not received my money....A full 3 weeks later!! I have called in 3 times to complain about this, and each time I was promised that the payment would reflect within 12 hours in my account.