Dealership client services

ONLY LEGAL ANSWERS PLEASE

I gave my car to the star nissan weskus agents vredenburg cause it was not starting, they did a diagnostic test and found the problem. They send the part to be unlocked and also to programme the keys and update the ecu. Agents put parts back into the car and still it was not starting. They called and told me their job on the car was done and also gave the qoute for their job that I need to pay and they will be sending the car to another company to check the wiring as the car is not starting yet. I went to the company who checked the wiring and they said their is no faults on wiering and they also did a test that states the car is not yet unlocked and the keys are not programmed. I did not pay the agents yet.. So my questions is am Liable to pay for a job that is not done by the agents correctly or completly stated by this other company???? What can the agency do to me if I refuse to pay? And what should my next move be legally??? This other company has made contact with the agents about this issue but they are not responding I have also called the agency a few times but they do not come back to me.