other than hammer away at BT. They probably take the view that it's not worth the effort for someone to go into the server and delete a few Mb of files, so they simply invalidate the login and forget about it.
If you can get them to validate the login for a day or so you could FTP into the server and do the job yourself, but that's like asking the BBC to delay the start of a program because you're stuck in traffic.
Have you tried to raise someone on the 'phone? A person to person contact sometimes works wonders.