Is the old fibre providers line used to bring in BT broadband from the pole or a separate one installed
Depends if old and new are both Openreach provided.
Eh?
Are you asking if Openreach will use an Alt Nets Fibre Drop Cable to Cut & Draw their own Fibre Cable?
If so then the answer is no. Openreach can’t remove other Alt Nets Wiring and or Equipment and neither can the Alt Net remove Openreaches.