virgin.net email account compromised and I cannot reset my password

Are you currently a VM broadband customer (sounds like possibly not from your description).

It is quite possible (likely) that VM is in the process of deleting your email address if you are no longer a VM broadband customer.

If you can still receive emails through an email app, you should backup your mailbox ASAP as you may lose access from the app next.

You should also set about quickly converting any online accounts which require access to the virgin.net address over to a new third party email address (while you can still receive email security notifications from providers while you switch email addresses)

If you have used the same email/password combo (that is now in the hands of the scammers) for other sites and services online, you should set about changing those to a non-VM email address and a unique password for each site as the scammers are likely to keep trying your other sites and services. Set up 2FA where you can.

I am not a broadband customer. I'd be pretty concerned if VM can delete my email account without notice. I don't recall any communication to that effect. I understand VM email accounts are for VM customers - but that they've allowed non-customers to retain email addresses - the same way Gmail and Outlook have. 

I still have much connected to my VM email address. I need to get back into it in order to approve changes to move to another address - but more importantly, to stop the hacker using my account!

This username and password combo is only used on my VM email account, so I am even more interested to know how they have managed to get that one password, and not any other I have. I have 2FA on everything, but have never managed to get it on my virgin.net email account. 

Have a scan through the many similar topics on here and you will see that VM is actively deleting legacy accounts that are no longer linked to a current VM broadband subscirption.

At best VM might grant you temporary access for a rescue mission to retrieve data from the account for archiving (though this tends to be offered to recent customers who have recently closed their broadband subscription).

You should get a reply from a VM forum team member here, usually within a few days but seems to be taking longer just now due to a high turnover of email topics recently. They may try to get you temporary access or may just offer to get the account deleted.

In the menatime I'd suggest you start switching over to a third party email ASAP if you can still receive incoming email for security change notifications and try to get one step ahead of the scammers.

Even if VM does give you temporary access to the account it won't be long term or permanent without a VM broadband subscription.