I Ender I wrote...
i know everyone is ticked off that this happened, but i dont think you're going to get much in the way of personalized respones at the moment. Give them some time to figure all the kinks out before they can respond.
Maybe go play the game a bit to check out the new classes before you start making rash decisions and creating multiple accounts to try and fix the problem yourself. I know that doesn't make up for whats happened, but at this point there is not much the gamers can do.
I dont think Bioware, EA and Microsoft will leave you guys out to dry, so for now give them more time to make sure the problem is definitely fixed before they give you a definitive answer.
Just trying to help 
Silly Ender, patience and reason don't belong on the forums during Launch Day!
But seriously, for all you folks making secondary accounts and whatever to try to work around your issues... keep in mind all of these redemption codes state pretty clearly that they're one-use only; in other words, be careful what work-arounds you try.
For those of you just finding you can't access the Cerberus Network in-game, if you haven't, I'd suggest trying to redeem your DLC through the Social Networking site (available under Profile > Redeem Promo Code). I have yet to connect to the Cerberus Network in-game, but I was able to redeem, download and install everything through the social network without a problem.