Welcome to our Community forum and sorry to hear that you've lost access to your email account. I'm afraid that email address that have no active Virgin accounts are deleted after 90 days after disconnection and the deletion cannot be reversed.
I really am sorry that you was not made aware of this and will feed this back to the relevant team and make sure that it's briefed out.
The staff can't do anything but delete the address and mailbox more quickly, but I can give you a few pointers.
Were you using webmail to access your emails? That is usually the first thing to close, but the mailbox is still in the server.
First check your address using mailtester.com - if the result is RED/does not exist - you have no chance. But if GREEN-valid, then you can retrieve something by using an email client (programme). Try Thunderbird which is free and easy to use. You will need to know the password.
Then you can back up and get ready for a better email service - choose one with better security, better support, better spam filtering.