Are you a BT broadband customer?
How long have had the email account for?
Were you paying for the account?
Our BT Premium Mail service is generally used when you don't have a BT Residential service and want to keep your email address. It's also sometimes used when you move to a BT Business account and want to keep your residential email address.
I can't make any promises but I do feel it's worth us double checking to see if everything has been done. The talk of migration worries me as there hasn't been any movement on that in a while. You can get in touch with us by clicking on my user name and then on contact the mods. It's on the left hand side of the page.
You can always find out if your email is a BT Mail account or a BT Yahoo Mail account at the below link:
Just a thought, when you set up your email client as a POP3 account did you by any chance delete the account and then set it up again?