E Mail Accounts and Passwords (again)

A number of different issues mentioned in your post. 

Following the merger of NTL and Telewest after their purchase of Virgin mobile leading to the rebranding as Virgin Media a random blueyonder email address was selected as the primary username.  In my case this was an alias address rather than the Telewest generated username.  I suspect that the same happened to your account.

A recent security change made by VM means that the primary account holder can only delete secondary accounts rather than being able to generate new passwords.  Each VM or Blueyonder email address now has its own My Virgin Media account where changes to account details, passwords, telephone security answers and app generated passwords are created.  To access this you need to be signed out of any other VM accounts before signing back in with the email address concerned.

In order to access the secondary accounts via an email client such as Outlook you will need to generate an app specific for that email address.

VM have recently changed the log in requirements for accessing VM Mail via third party apps.

If you change the password for the account in My Virgin Media > Account settings > Account details you will not be able to use the new password to access the account via an email client. Email client access now requires an app specific password which can be generated in the MyVM > Account Settings > Account details > Mailbox App password management

https://www.virginmedia.com/dpb/help/change-my-virgin-media-email-address