engine damage after minor external panelbeating.

I took my car ( 2014 VW Jetta 6 1.6 TDI DSG) to Barneys Panel beaters to be repaired. The damages were minor external dents on 17/11/12. The car's front bumper was scratched and had to fix the rear and the front fender on the right hand side of the car. When handing in the car, an inspection was done and there was no engine faults to record as the car's engine was functioning 100%. I received a call to fetch the car on Friday 27/11/15, and I collected the car on Monday 30/11/15. While driving the car I noticed the diesel ignitor warning lamp was flashing. I immediately called the Panel beater and they confirmed I can bring the car in the next day. I explained to the panel beaters that I cannot take the car in the next day because I had to take my daughter in for an operation. I took the car in today Wednesday the 02/12/15. I was addressed by two men one of them said he is the manager they refused to assist me claiming that they did not touch the engine and that the problem is caused by wear and tear. As per Barneys manager the problem could have happened even if I did not take the car to them for panel beating. My argument is that I took the car to them for panel beating it