I'm sure I recall a thread about this a while ago, but can't find it now. As I recall, there was a problem with the Belkin firmware which was causing excessive traffic on the network, so VM were getting people to upgrade the firmware. As far as I know, it was only the Wireless G model, but it could be that a) the same issue is occurring with the Wireless N or b) it is a cock-up on VM's part.
If you phone VM again, refer them to
http://www.virginmedia.com/help/belkin.php