Welcome to the community forums.
Sorry to hear that an older blueyonder account has been hacked. If the email is not connected to an active broadband service then it should have been deleted within 90 days of you disconnecting. Sounds like the email is what we called 'orphaned' as it has no service connecting to it.
To complete a change a password request on it, we would have to see if we can transfer the email to the active broadband account, but this would remove any already registered email details, such as your My Virgin Media log in.
If you are happy to, and you have no important emails that you need from the mailbox, I would recommend we delete this completely. Please join me on private message so I can locate your account and pass account security. You can see your private messages at the top of the page, in the envelope icon.