E.g.With Sky it's this simple. If you are in the master and there is a fault there's no charge.
If no fault is found they keep sending out engineers until a fault is found.
So Sky see the engineer report, see you were in the master. You won't be charged.
Black and white and you know I won't get a bill.
You must have been lucky with Sky or the Openreach engineers were not in a hurry to move on to the next job.
I had a total loss of service on both phone and broadband service on/off for 3 months and after 3 Openreach engineer visits Sky did nothing.
The line had
no internal wiring/extensions, tested through test socket and still faulty,
no other devices connected and still faulty. Sky were less helpful after 1st engineer, were all but insisting that I would have to pay for the 2nd and 3rd engineer visit and then wanted nothing more to do with things after that.
I thought that I would mention that as a balance to your post.