Poor Customer Service

My car was taken for repairs and it has now come back faulty and puts me in high risk. I had reported the matter to the manager who handed over the car to me to report the incident but no one bothered to follow up on it. the car came back with an diagnostics showing that the airbag light was faulty. There was also water by battery which could have resulted to more damage and risk for me as the driver. I had to take it to BMW in Cedar in Johannesburg. They said it's a good thing I brought the car because it could have caused immense damage. I had to pay over R3000 to fix it. I want a refund of my money as it was not my fault. Please help to make sure Discovery which is my insurance and the panel beater involved to account for their negligence. This has caused a huge inconvenience as i had to commute for a week and also suffered financial loss!!