Where have you reported this user? Through the Origin client?
There is a dedicated email address for ME3 reports (ME3MPCheaters@BioWare.com), but I don't think that's still active.
This exact thing happened to me when playing today, player joins session as the cerberus adept and begins to spam pull to the point that i am effectively useless. It also happened to me three rounds i a row too. The solution that i came to (and i realise that it isn't a perfect one) was to just host my own game lobby so i could have full control over the teammates that i would have for the round and in the event that he did join would be quickly booted from the server.
Unfortunately at this stage in the games life cycle i would think that it is very unlikely that a player like this would receive any kind of penalty for this type of behaviour, it's just unfortunate that there are players like this that will go out of their way to "troll" and ruin everyone else' fun in the game just to get their own sad little kicks.
This game is still actually very fun to play, even after playing it for so long it is still my personal go to horde survival game when i just feel like unwinding, it would be unfortunate to have to cease to play it if this issue were to somehow spread, though it honestly wouldn't surprise me if it was the in fact the same player.
