in theory, BT broadband is a seperate company from the BT wholesale or Open Reach engineers who come out and do infrastructure work.
In practice though I think some ISPs get preferencial treatment, maybe BT broadband do, I certainly felt IDnet did when I was with them.
I don't know the reason....maybe some ISPs take special care not to make unnecessary work for BTw or something.
I certainly can't think of anything concrete to help you, except...maybe....some concrete
There are 10 kinds of people, those who understand binary and those who don't.