You have come to the right place, dmhg. Has it been more than 90 days since you ceased your broadband services?
As you know, the mailbox should have been closed AND deleted automatically 90 days after you finished being a customer, according to VM's own Terms and Conditions. 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 friendly Forum Team will visit this thread in the next few hours (or days?) and then take your personal details by private message.
When they say it is done, you can verify it is gone by running the email address(es) through mailtester.com.
In the meantime, if you still have access via an email client (Try Thunderbird - using IMAP process which synchronises with the mailbox stored on the VM server), delete everything from all the folders to reduce the information available to hackers.
Thank you for your post Dmhg and welcome to our community.
If the email address is on an inactive account we can ensure this is deleted for you, it would need an IT ticket to our team which would take up to 5 working days to complete.
I'll pop you over a private message now if you could please confirm the email address and as much of the account details as possible so we can put this through. You can respond to this by going to the purple envelope in the top right of the screen.