I have exactly the same problem.
Have read all the threads and tried all the powering down and resets imaginable. Waiting for a mini hub to be delivered and engineer to visit. Even had my landline phone ringing many times with just loud noise on the phone when I pick it up.
I had been stuck abroad for over 2 years and only returned to the UK a few days ago; many times while abroad my smart devices would not connect for days even after many BT router resets.
Thank you for posting. I'm sorry if you're having problems with your connection. If you can hear a loud noise when using your phone and along with the orange light on your hub, it would indicate that there is a fault on the network.
I understand that you have an appointment for an engineer to visit? What date have you been given for the appointment?
An engineer is due on Monday.
Thankfully a mini-hub arrived this morning (wonderful service by BT and DPD) and so I have connectivity.
He had to go back to the green box and the fault was beyond that underground. Had to wire me up afresh after one of the wires was broken. Connection is stable and I have a dialtone.