As John said, don't overlook the necessity to file your complaint in writing in addition to the phone calls.
I discovered years ago that dealers really hate it when a customer writes to MBUSA. It causes the dealer to have to respond in writing to the complaint and to have to provide a lot of paperwork.
The combined telephone/writing campaign to MBUSA, always being courteous but firm, should yield the results you are seeking.
You are entitled to more than what you have gotten. Hang in there. Good luck.