GM imperial Vereeniging has been fixing my vehicle for three months now!

My vehicle was overheating while I was on vacation on the 02.12.2018 in kzn my car was towed in at Umhlanga GM then I was given a curtesy car to come back home in Vereeniging then sometime late December they called that my vehicle has been delivered to GM Vereeniging, I went to collect it as I drove out it was overheating again then I called them to come collect it again, they said because they don’t know what Umhlanga did to the car they will call them and find out what had happened. A day later GM Vereeniging calls me to say that my vehicle engine is damaged and they are going to get authorization to fix it, two weeks later I call to find out what was happening I was told the people are on leave and nothing had been done, I called customer care they had no clue what was happening and the person who was handling my case was always either on lunch or on leave but never called me back, I then asked that the manager called me which has never happened till now and as I speak to you my vehicle is still with them and I have no idea what is happening. Please assist!