04-12-2011 14h43 - edited 04-12-2011 14h45
Just call 0800 800 150, have your account number handy, and select broadband, billing.
Or try live chat here, follow the links http://bt.custhelp.com/app/contact
Forumhelp (personal website) is back online with lots of useful info for BT customers. Some links may be out-of-date, but I will update them when I get time.