Take it back and demand that they correct there mistake. If it was not like that when you dropped the car off, then it is there fault.
If they are having problems in the first place, than this will be nothing new to them. Also, I suggest you find another shop in your area for future repairs/services, run a search in the "Good MB Shops" section for a possible lead.
96 C280, [Green]Greenish Black[/Green]