Sorry to hear of the email access issues and thank you for raising this via the forum.
Can you confirm if you are still a Virgin Media customer with active services? If you have cancelled services recently, or maybe even a while ago, the email address may have been closed as these are for active customers.
If not then we will be happy to look into this further for you. Have you hand any correspondence from us in regards to the email address and unusual activity? This can result in the mailbox being suspended and the internet security team may even reset the password on the account if they feel it has been compromised.