I am not receiving good service from BMW SA

I have reported an irregular sound coming from the wheels and I have taken my car to the dealership for check. The car has been with them 3 times and they seem not able to diagnose the problem. I use a car for work and I am incovenienced because my job is affected. The dealership can't offer me a courtesy car because they say they don't have any. I took the matter to BMW SA but they also are not giving me any joy. My car is still under maintained plan. They promised to resolve the matter for me but they never update me with the situation. I always have to call them if I need update and they still haven't done anything about it. They said the matter is escalated to their senior management but still there is no difference. I am really not comfortable driving with this car especially for long distance since I dont know the nature of the problem.