Appalling service

My Chery J2 2013 model, was bought last year January, I have had numerous problems with it since buying it from the clutch that had to be replaced TWICE! to the back passenger window not closing completely to now that the car is switching off while driving with no warning whats so ever. I had the car towed after 3 hours of waiting on the side of the road to the closest Chery Dealership. They indicated to me that they do not know what the problem is and that they have fixed the problem the car shouldn't switch off, How can a problem be fixed if they don't know whats causing it? I don't understand this *******. They said that they need to keep the car overnight to make 100 % sure it doesn't happen again. I collected the car Friday 27th Feb 2015 at 19.15pm at the dealership and was on the highway when the car went dead, luckily I could roll down to the off ramp and had to car road side assistance once again, So what problem was fixed if they didn't know what was causing it? What if something serious had happened? To this day my car is with the dealership and I have to keep calling for feedback, where is the customer service? why are they selling cars that are breaking down s often?