Same thing happened to my C280 few months ago. The previous oil change was done at a dealer as a promotion ($20). However they had the drain plug on too tight. I swore to myself that I would never have anybody else change the oil for me again.
The solution? I went to an Econo oil change store and they managed to take the plug off with vise grip. I was charged $10, including a new plug. I thought the new plug was as good as OEM parts so I didn't bother to go to the dealer to get another one. Other oil change chain stores (like Jiffy lube) would do that for you, I guess.
By the way, they took out the old plug, and put the new one right in, without loosing much oil (about 1/2 quart). So I drove my car home and enjoyed the oil change.
Harry (94 C280)