Are you/your partner currently VM broadband customers? If you are, there may be a possibility of rescuing the mailbox and associating it with the VM broadband account (but there are conditions to be met to do that and you need to engage with a VM forum team person on here to go through the options).
If you/your partner are not with VM for broadband, then you have more of a struggle. You appear to already have seen the topic here
https://community.virginmedia.com/t5/Email/virgin-net-email-swindle-Tell-BBC-Rip-Off-Britain/m-p/5586294#M281331
where temporary access was regained via ICO and DPO. There is a second post here
https://community.virginmedia.com/t5/Email/EMAIL-ACCOUNT-CLOSURE-RESOLUTION-virgin-net/td-p/5589588
where the customer got a different outcome via the VM executive team. You will have to search for the email address as it gets removed if posted on here (even though the address is in the public domain on VM's own web help pages). You may be able to regain temporary access via that route. Unfortunately though, you may not get the same outcomes via either method above as VM is so inconsistent in its support responses.
I would suggest speaking to the ICO in any event, if for no other reason than to log what VM is doing. The more people that do that, the greater the chance that the ICO may take an interest. IMHO it is not right that VM is closing these mailboxes without notice given how important an email address can now be to a person's identity.
The general pattern of these closures seems to be that, to begin with, the mailbox enters a 'locked' condition where it still exists but is inaccessible to the user. Later on it becomes permanently deleted and cannot be recovered. As per the first link, it appears it may be possible to regain access from the locked condition in order to rescue data and change addresses etc.
I hope you can regain access and recover your data.
