Well, the obvious thing to do is find another dealership. Considering where you are, that shouldn't be all that difficult.
When I first read your thread title, I was expecting something really awful, like a mechanical problem. You're stuck in the "endless-dealer-who-doesn't-really-want-to-help-loop". Start by looking for another dealer to work on the car.
Secondly, there are at least a couple of threads rattling around someplace either here, or at MBWorld.org, that list the names of just about everybody who matters at MBUSA. Do a search and see what comes up.
Thirdly, in a situation like yours, you should ask to talk to the General Manager of the dealership - explain the problem and your unhappiness - sometimes, this is all it takes.
I just found one of the posts I was looking for:
Victim of Fraud - MBWorld.org Forums