Bad service and passing the buck

My wifes car has got 17 000kms on the clock and is only 5 months old. On the 4th of May 15 my wife was on her way home to Hartbee****rt dam where we stay when her car showed her a warning signal 'drive train' and she could not drive more than 70kms per hour. We took her vehicle to bmw Cedar Isle the next morning. On Wednesday the 6th we could fetch her vehicle again as Bmw told us that they did diagnosic tests on the vehicle and that the problem was fixed after they had reset the vehicle, they test drove it and everything seem fine. On that same day again when my wife was on her way home the same signal came on again. We returned the vehicle again the next day. Now 5 days later they tell is that there is a problem with the turbo and that it could take a week to fix. We are still not able to get a courtesy vehicle for my wife and we need to rely on other people to drive her and my two sons around as i have to work away far distances from home. They keep on passing the buck and i am the one to phone each day to find out what the progress is on this vehicle, and and to follow up on a courtesy vehicle for my wife.