If you received a text message with the link (http://vm.tmce.biz/wap4?app=virginmobile&c=vir&NEXT=P23
) then you used over 2.5GB in December, otherwise, you shouldn't have any issues.
To be honest, it isn't that bad. $25 a month for just data on AT&T only gives you 2GB, and now you can't even get the $25 plan anymore. It's just a sign of the times. Besides, I'd rather be throttled than limited.