In reply to a post by hk11:

Calls are related to line rental and not BB.

In reply to a post by RobertoS:

Call plans and any other phone charges are always with whoever you have the line rental with.

Not necessarily. EE/Orange used to do BB Only + a Calling Plan (Anytime, E&Ws or W/end only) to anyone with a BT line. Line rental still went to BT (or other). I can still upgrade to one of those as I have BB only from EE. Perhaps the OP is on one of those?

At the time there were other ISPs doing similar, but I can't find any today.