Can I take it that you don't have a current broadband account with Virgin Media?
The issue is that using any of the VM email accounts (virgin.net, ntlworld.com, virginmedia.com or blueyonder.com) is provisional on you having a current broadband account otherwise the mailboxes should be deleted a couple of months after you leave.
The situation regarding the virgin.net addresses is slightly more complicated, but the above advice is still true and the likelihood is that the mailbox has either been deleted or is in the process of being deleted.
I would assume that the other mailbox isn't long for this world and if you do still have access to it then you need to copy out any emails that you want to keep, as once it's gone, it's really gone.
Naturally, if I have misunderstood, and you are a current VM broadband customer then, the forum staff should be able to assist with this when they get to this thread.