I'm afraid, there is no long term solution for this. Once your mother left VM, then her BlueYonder email address and mailbox should have been deleted after about 90 days as per the Ts and Cs. Unfortunately VM can be a bit lax in actually doing this on schedule and the mailbox carries on working, the ex-customer just assumes that it always will do so and blithely continues to use it.
Until the day comes that it gets caught up in a periodic cleanup and disabled and eventually deleted with no further warning. And this can be many, many years later - which would seem to be the case here.
Now there is a slight possibility that a member of the forum team can intervene and check the status of the mailbox and maybe, and I must stress maybe, restore temporary access to it. But again I have to stress, this will be temporary and a one-time only offer. But it should be sufficient time to copy any emails she wishes to keep and notify all contacts of a new address.
VM have no facility to pay them to just maintain an email address, and indeed they have recently stopped creating new addresses for new customers entirely. Also the person who said, you could somehow buy the address from Virgin is wrong - that simply cannot be done as it isn't the way that email works.
I'm afraid you have to start the process of getting her a new email address (a free one from Gmail or Outlook will be fine), hope that VM can give temporary access back and start the process of moving over to it.
