I've been through dealer problems in the past. I believe that there is an issue of typical human nature. Typically, people will be nice and put up with BS. Many people in all businesses get accustomed to this. This allows people to get by with shoddy attitudes in many cases. If you elevate this to the area MB representative and let them know in no uncertain but polite terms that you are not happy, you will get satisfaction at some point. If the area rep doesn't get the job done, email the CEO of Mercedes Benz and cc everyone you know of within the dealer and Mercedes Benz.

Good luck,