NOT unusual. If you do a search you will find some "horror" stories just like yours. However, not ALL the MB dealerships are that way. For me, an independent, is the way to go but, in a new car?
You would think the best cars in the world deserve the best customer service in the world. WRONG! That is why Lexus and some other car manufacturers are concentrating on customer service/satisfaction and getting some of the MB market.
You already tried the right way to do it, now is time for your voice to be heard, call/write the BBB, consumer groups in your area, TV news consumer protection person (if there is such a thing), etc, etc.
I feel for you G-man. Shame on you MB, when are going to get it?