Charged For Services Not Rendered

Brought my car in for a major service. I had issues with the car over heating and returned the car to them three times in the same week with them failing to find the problem. I found out they charged me for parts in the car they never even changed after those parts became faulty in just a couple of months. My service was on the 25th of March 2015. When i returned to them to complain, they are not taking me seriously because its almost three weeks since i complained and no response from them at all.