When complaining, I have had best results when I try to put myself in the company's shoes and keep personalities out of it. The assumption is that no one wanted you to get a bad car or a bad repair, it just happened, and that you are doing them a bit of a favor to report the problem before you conclude that your car is a lemon or that all dealers are incompetent. I can say only this: I was never able to find an honest RENAULT dealer.
Tell them exactly what happened that you did not like, and describe exactly what remedies you want them to take that would please you entirely. Do not skimp, it's not your money; but be realistic.
It is best to write a letter, since this way both you and MBUSA and the dealer (and possibly your family lawyer). Enclose copies of all mail sent this far and make a copy of everything sent. Sending a letter Certified Return Receipt Requested generally gets maximum attention if addressed to the person in charge, while jabbering on the phone gets an underling who is poor at taking notes.
Be courteous, but insist on a resolution to the problem: insults generally aren't useful in getting things done.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"