Thrifty Not paying back deposits

I rented two Nissan NP300 and had to pay R9500,00 per vehicle as deposit because I paid with a debit card. The one vehicle has been taken back three weeks ago and the other now 14 days. I have phoned their call centre and left numerous messages. No body is phoning me back. I have now contacted the branch manager where i got the vehicles and he is also not very helpful. (Centurion branch) Its a pity that their aftercare service is so bad because the poor guy renting me the vehicle was very pleasant to work with.