The mailbox should have been closed and deleted automatically 90 days after you finished being a customer. But the process fails all too often and leaves the former customer vulnerable to hacking and theft of personal and financial details (IMO, someone should definitely claim for damages from VM or complain to ICO!)
Only VM staff can raise a ticket to get the mailbox deleted manually. The Forum Team will visit this thread in the next few hours (or days?) and then take your personal details by private message. Best wishes to you.
Welcome to our forums and thank you for posting. I do apologise that your account has been compromised and you've been unable to have this removed.
As MissPasko has said, we're more than happy to raise this with our IT team for deletion. I'll send you a private message now to clear security on your old account, please head to the purple envelope in the top right corner to respond.