Are you a BT Broadband account holder or are you buying access to BTWifi-Fon?
If you are a BT Broadband account holder you need to use your BTID and password to access BTWifi-Fon.
If you are a "long standing" BT broadband account holder, ie over 5 years, you may find that you need to use your "master" BT email address and password which is not necessarily your BTID.
See link how to log on:-