You were told a fib to get you off the line. Bear in mind that many call centre operatives seem to be measured in terms of – calls closed down – as opposed to the better measure of – problems solved. This is particularly true of outsourced call handling operations in overseas locations.
Whilst, in principle, it may be a sensible security precaution to change passwords at regular intervals, one would need to use a password manager to properly manage anything more than a trivial number of passwords – avoiding use of obvious or easily-remembered passwords.
VM’s main advice on password management is to be found here -
https://www.virginmedia.com/help/how-to-create-a-strong-password
and says -
“It’s up to you how often you change your passwords, but it's generally a good idea to change them every few months.”
Like many others your password may have been changed by VM as the result of a security trigger. See the recent spate of – email locked – mailbox unavailable – etc reports.
Wait here for the Forum team to pick up your post and investigate if necessary.
