Poor quality service provided by Car Care Clinic

The service I have received from Car Care Clinic in Vanderbeiljepark is very bad. On the 27th May 2025 I took my car inn for service 60000km .My car was running smoothly before I took it in there, so just after I collected my car there it started to give me issues, I have called them and explained to them regarding the problem that is happening on the car and they advised me to bring it back so they attend the matter..Upon my arrival on the workshop I found the other guy with the very same brand of the vehicle I'm driving with the same issues that I'm experiencing with my car. They said it was because of the bosch sparkplugs they fitted on the car and they will remove them and fit NGK sparkplug..So after that I drove my vehicle home and it did the same problem, then I called them again to alert them that I'm still experiencing same issue with the car.They then requested me to bring in again. I did take car in and the check the car once again and now they telling me the a different story...They assuming it might be the combustion and that I will have to pay R7500 for them to fix that problem. I don't understand why is this car doing this after they did the service, and I asked them why should I pay them a amount of R7500 for something that was not existed before they work on my car , they failed me this guys.