There is some debate as to whether there is a formal community manager, but the person ostensibly doing that job doesn't really deal with the forums or support issues.
Most likely, EA help meant to suggest that you contact the developers through the community forum (which was good advice a couple of years ago when the developers were still using the forum.)
The problem you're describing is a lingering one, and requires one of the developers to manually reset the challenge on your behalf. Since the team has moved on to other projects, they aren't really doing that anymore. The developer principally handling resetting challenges was Bryan Johnson. He's working on another game, now, but he does his best to keep tabs on the MP forum, and when he is available, he will still reset challenges for people.
I believe he is knee-deep in QA right now, so he probably won't be regularly checking the forums in the immediate future. Your best bet would be to PM him. It could be a while before he is able to get back to you but he is very good about following up on issues once he is aware of them.
Bryan Johnson aka "Brojo"
You can click that link to get to his BSN profile, and use that to send him a PM. Mention your Gamertag, platform, and which challenge is stuck.