Are you a BT Broadband customer or are you paying for your email through a BT Premium email account?
If neither of the above your email accounts will be downgraded to the BT Basic email service.
If you are a BT Broadband customer, are the email accounts that you have been informed are to be downgraded set up from this BT Broadband account or were they set up on another BT Broadband account such as a parents account or a previous BT Broadband account that you may have had then left BT and subsequently returned but continued using the email accounts?