Dollar Thrifty double charged deposit and never paid it back

I hired a car with drive SA and they instructed me to collect from Dollar Thrifty in Midrand, Dollar Thrifty told me to pay a deposit of R2000. Upon the return of the car, Dollar Thrifty did not return my deposit of R2000 instead charged me another R2000. I have tried to no avail to complain to them and they still have never paid my money. On top of that they charged me an extra day's car hire which was caused by their own fault. Dollar Thrifty have ****** more than R4000 from me.