Mccarthy Audi pre-owned vehicles

I have taken my car back to the dealership after one month of driving it because of a faulty engine, I have been given a courtesy car for four months now. I am getting excuses on why the car is still not fixed, they are giving me false date as to when the car will be fixed. please assist in this matter, I bought the car from a dealership called Mccarthy Audi pre-owned in Pretoria Wonderboom a Kia Rio 2017 model. They took the car to a local mechanic instead of a car workshop, they are not taking my calls anymore. I wouldn’t recommend anyone to buy into that dealership.