Welcome to this user forum.
Swapping now would introduce lots of delay, as all existing connections would have to be ceased, and you would start from beginning again.
BT Retail do not provide or maintain the external network. This is done by Openreach (A BT Group Business) who work for all Service Providers apart from Virgin Media. BT Retail do not get any special treatment.
The broadband task cannot be issues until the phone has been activated, and closed off, as its needed during broadband commissioning.
Openreach are very busy at the moment, but are trying to get people connected by Christmas.
What did you order, normal broadband or BT Infinity?
Openreach now cease fibre connections when a change of provider takes place and that can cause delays particularly if the cabinet is full as the port is allocated to the next waiting customer regardless of their provider and it can cause activation delays while waiting for capacity increases on the cabinet so changing provider could increase the wait even more