I used to be a virgin media customer along time ago. I have used my virgin.net email for the last 25+ years! It's suddenly stopped working.
I am afraid that the bottom line is that in order to continue using a Virgin email account you need to have a VM broadband account.
If you have been using your virgin.net email account for 25+ years it was almost certainly part of the old dial up internet service they started in 1996. In order to keep using that service you had to dial up at least once every 180 days but that service was closed in 2013.
According to Virgin Media's (or NTL as it was originally called) own terms and conditions unless you subsequently took out a broadband contract with them VM should have closed that virgin.net email account years ago
It seems in the past VM were very lax about closing email accounts which has resulted in people like yourself continuing to use them for years. However, as you have found, they now seem to be deleting old email accounts such as yours whenever they come across them. Sadly, they never seem to give any warning before doing that.
Unfortunately, if you are not currently a VM broadband customer then VM support staff are not really able to help you.
You only say that the account has "suddenly stopped working" and without more detail such as the error message you are getting it is difficult to be specific about your options.
However, in truth at this point the best advice I can offer is to try resetting your email password from here: https://my.virginmedia.com/forgot-details/password to see if you can regain access to the account. Enter your virgin.net address as the username and follow the prompts.
If you get an "Unable to find username" error message that means the email account has been deleted. If so that's the end of the road I'm afraid.
It sounds as if you already have another email account set up but if not then you really need to do that asap.
Sorry to be the bearer of bad news.
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