Bad service

In 2018 February i bought a Mercedes Benz C*** model, silver from Driving Force. The salesman then was Charl. I took the shortly after i bought it to the Northern Cape. The car broke down and after many conversations with the dealer i had to get the car to Cape Town, which I did. I took the car to their workshop for repairs but they could not find the problem. I told them what the problem was and that they must fixed it. I was told that they cannot fix If they do not find the fault on the computer. The mechanic even drove my car for two days and could not find the problem. Again i told them what the problem was but still they did not wanted to fixed it. Say i must drive the car until it gives problem again. Im Sunday 2019/09/29 the car finally broke down again,the same problem. I phoned Barry the manager of Driving Force for help. He said it's too long ago and cannot help me. I must fixed the car on my own cost. I feel that if they had listened to me a year ago, this could have been avoided. I want them to fix the car as it would cost me R11 000.