@barden44 correct about phone numbers but email simply doesn’t and cannot work in the same way. Put simply an email address belongs to and is controlled by whoever owns the domain, ie the bit after the @ sign. Virgin Media own the blueyonder.com domain and hence own all of the email addresses, they simply ‘allow’ you to use one based on certain terms and conditions, ie be a broadband customer. It is just not technically possible to ‘move’ a particular address to another email supplier.
Now, of course, VM could offer a service whereby they keep the address live for a monthly fee, but they have decided not to do this - fair enough, their company, their system, their rules.
The only way that an email address is ever truly yours is to purchase your own domain and email storage and manage and maintain it yourself.