Poor service

I took BMW 320i F30 and according to their diagnostic test they replaced high pressure fuel pump and the car came with rough idling and I paid R11000 different from what the warranty(R8000) paid and were told that they need to open the engine and check what could be the problem which was disappointing to me because I trusted the dealership with their high caliber systems they possess and I took the car to another workshop they were able to detect the problem and now after the warranty authorization they busy fixing the car.