Fix one thing then break another

I brought my vehicle in for repairs on 13 April 2016. The work was completed, but it effected another system on the car: The exhaust flap stopped working.<br> I was asked to return the vehicle, which I did on 15 April. When I collected it on 18 April, the service consultant (Gavin) commented as a result \Check exhaust flap. Unable to fault.\"<br> The exhaust flap STILL does not work, leaving me with a driving experience that is accompanied by a constant \"drone\" from the back of the car.<br> It is unacceptable that technicians as highly trained as BMW's should (1) somehow cause other systems on the car to become inoperable and then (2) come up with a conclusion that assumes the customer knows nothing about the technical aspects of their car. <br> I phoned the service manager (Ashraf), who was not available, and was told he would return my call.<br> I expect this problem to be properly addressed, and I am willing to take it up with BMW in Germany, if necessary."