Hyundai service center broke my vehicle

I sent my car into Hyundai the Glen for a service on 06/10/2018. After the service the service agent calls me to say that my car does not want to start, give them till Monday to fix it. I call on Monday and I'm informed that the ECU has blown, hence the car wont start and that I'm liable for the ECU cost of R12 000. My car has given me no problems over the years, and now suddenly during a service a component blows and I'm responsible for the cost? That is absolute nonsense and i will not pay for something that i did not break. Hyundai the Glen has terrible service delivery and it it their responsibility to bear the cost of the component that they broke.