Unfortunately, I don't think this is something you can resolve yourself. A number of posters to this forum reported that problem a few weeks ago along with similar issues with the Vacation Notice option.
A ticket (F010421780.) was raised with the relevant VM IT team at the start of February and since then reports of people seeing that issue seem to have died down. I am not a VM member of staff but I will raise the question with the VM Forum Team as to whether that ticket has been closed.
"really tough time with 2 secondary account on Virgin.net. I've set up new account with another provider"
So are you still a VM broadband customer? If you are no longer a VM customer I would hesitate before setting up an Autoforward to your new email account. You might live to regret setting up that Autoforward!
The reason I say that is if you are not a VM customer it means your Virgin.net accounts are not linked to a live VM broadband account and so VM could remove access to those email account(s) at any time.
It is very common for ex VM customers to post on here complaining that their old VM email accounts are continuing to forward spam and scam emails to their new (non VM) email account and they cannot turn off the auto forward because VM has removed access to their old VM account.
That's something to consider.
I'll report back if I get an update from the VM Forum Team on that IT ticket re the forwarding issue. Just to update that, it would seem that the issue has now been referred back to the relevant VM support team.