Poor Quality

My M4(2015 model DFD706L) was involved in an accident on the 28/04/2015 ,it was repaired through the prescribed and accredited auto body repairer, after it was repaired it was taken to Modern Autohaus for quality check and motor plan re activation.On the 30/11/2015 the car had a breakdown took it to the dealer in Polokwane ,since that time I was not offered a courtesy vehicle.I was informed that the vehicles engine has to be taken out and an assessment has to be done to verify why the engine failed,but they suspect it as because of the accident .My question to BMW SA is what is the purpose of the quality check after the accident because clearly they should have picked it up that the repairs done where not done correctly .I have paid R1.3M for a vehicle with +-7000km which the dealership cannot warrant and they want to pass the buck. That Sucks BMW considering that this is not my first M vehicle that I have owned.Put anew engine so that I can go on holiday with my family and stop wasting my time