Looking back at your previous posts I can see that there may have been a misunderstanding last September regarding security changes that VM made to sign in usernames.
Each VM email address, including ntlworld.com, now need to have a third party email address linked as the sign in username. It is up to the user to decide what third party address to use. It would appear that you chose to use a mail.com address as the username for your ntlworld.com address. You could have chosen an address from any email provider eg. Gmail or outlook to mention two.
Unless your wife has had reason to change any of the details for her email account such as the password she won't have triggered the need to set a third party username.
I also note that you were going to close down your VM broadband account because you were unhappy about issues that you were having. Did you go ahead and do that? If so your ntlworld email addresses should be closed down 90 days after you ceased to be a customer.