Unsatisfactory service

I took my car for a service on the 11th of Dec 2015 I was told that that some parts needed to be replaced and ended up paying R 7500. My car got stuck on the 21st Dec, another assessment was made and I was informed that more parts must be replaced with a bill of R 12 292.50. I paid a deposit of R6000, the car is still not repaired and every time I go to the garage I'm given a different excuse and a promise that my car will be fixed the next day. Its been a month since my car is not repaired.