Following up on this: http://forum.mechlivinglegends.net/index.php/topic,11550.msg325310.html#msg325310
Supposedly, I should have gotten a reply yesterday. But, they're on it. Yay. Go EA.
I've finally got a working key. Had it for a couple weeks now. The EA "expert team" never got back to me, so I took to pestering them via support chat every few days, asking for a status update.
One of their supposedly Indian reps probably felt sorry for me, looking into the history, and finally offered me a new key. Copied it into Cryhammer -> "key invalid". I even tried it in the actual game, just to be sure. The guy naturally didn't believe me and advised me to reinstall. Ok, thank you, good bye, next try.
Told the next guy my problem, after lots of dicking around he too offered me a new key. Same old, marked invalid, not working ingame. Got told to contact my local (german) support by phone.
This is where I finally got lucky. The support agent there not only seemed to have a grasp of how computers work (i.e. no idiotic "reinstall manually because your key is bad" blah), but he gave me two keys to try. The first one he pulled fresh out of their database, and surprise, it didn't work.
Since the agent was an avid mech fan himself (he said he'd played MWLL and was in MWO beta, talked a bit about CBT as well) he dug a little deeper and found another old key somewhere - I have no idea how, sounded like it was attached to an older ticket or something. It supposedly came from the same database, but was generated ages ago.
That one finally checked out in Cryhammer, and also worked ingame. Woo. The odyssee was over. Only took over a month. I can see how that would put off most people from playing MWLL.TL;DR advice:
1. Don't bother contacting Steam support unless you're going for a refund. Contact EA via chat (choose "Crysis 2" on their website to get the live chat option) or phone.
2. Phone seems to be the best option for support.
3. Don't give up on EA support if you get a bad customer rep. Just keep calling/texting. I could probably have accelerated the whole thing by just contacting them back to back until i got someone on the line who would give me a new key.
4. Since a large portion of (or all?) new keys seem to be fubared, the least painful way is probably to get a refund on Steam and buy the box.
Would be nice if the OP could add this info to their post.