I'm in the same boat. I bought the Onslaught DLC for my nephew and myself (it's the only online game mode he's allowed to play), and it appears as though I just threw $30.00 right in the toilet.
"Fool me once, shame on you. Fool me twice, shame on me!"
I'll not give Activision any more of my money...ever!
While there isn't a plethora of honest XBox gaming companies out there anymore, there are still a few, and they'll be getting my hard earned money from now on.
There are far too many kids who's parents will buy them whatever they want, when they want it, and as long as companies like Activision can make money putting out cr@p for games, and stealing from people (via the DLC), they'll continue to do it.