Now this may sound daft, but BT is your service provider isn't it? If it
is an OR provided circuit but your SP is NOT BT then the system will
define it as not BT and thus fibre as not available because they do not
know what your SP is planning.
Try
ceoemail.com to find out the name and email address of the CEO of
BT. From personal experience I can advise that most CEO's in big
organisations like BT have their own team for investigating different
aspects of the business. Your complaint/query will be passed to the
relevant person and you will likely get a direct response with 48hrs or
less - I least I did!