drop the car off, get a loaner, and tell them to call you when it's fixed. If they call you and say they can't fix it, do not pick up the car and call BMW. I would consult a lemon lawyer as well.
If you finance or own, I would certainly take action. That would kill resale.
I cant believe you dealt with this issue for so long.
2010 135i - Alpine White - Coral Red- Glacier Trim - Bluetooth - ///M Sport - Paddle Shifters