Battlefield: Bad Company 2 Serial Key already in use

Hey,

I purchased Battlefield: Bad Company 2 a while ago. To begin with, it worked perfectly. However, when I uninstalled it and re-installed it on my computer, it said that the key I entered was already in use. I'm now unable to play the game. I posted a similar message a while ago on answer HQ, but EA seems to be ignoring it, or not noticing it.