You would be having the same 'problem' regardless which service provider you use, the £129 or whatever a service provider charges for an unneccesary call out , is only raised, if you insist on a visit, and the 'problem' turns out to be on something your provider or Openreach are not responsible for.
In this example, phone not ringing , what if the telephone instrument was faulty , or the 'ringer' had been turned off, IMHO, checking that the phone is OK and trying the master socket, is such a simple thing to do, that if OR are called out ( via their provider) and the OR engineer points out the ringer in the off position, turns it 'on' and the phone now works correctly, then a charge is totally justified.
If , when your provider tests your line, it seems there is no 'fault' , warning the consumer of the potential for charges seems OK to me, if you have done the simple checks ( equipment fault free, tried in the master socket ) , then you can disregard the warning, the alternative would to say nothing about possible charges and them present a bill when the fault is your own 'faulty' equipment.....what would you prefer ?
If you called a garage out to look at your car because it wouldn't start, and the garage said 'are you sure it's got fuel in it' and you said ' I presume it has, but the car has a warranty so come out anyway', the mechanic attends and finds the problem is you are out of fuel, the garage would still want paying for the mechanics time, and your warranty company certainly wouldn't cover the cost
There is no excuse for poor customer service, and many complain about not being able to make themselves understood , or being able to understand offshore call centre staff, but at least BT have committed to having 80% of calls into their organisation answered by staff based in the UK, and that is welcome.
I can only imagine that when you reported your line BNR ( bell not ringing ) initially , there was a detectable external fault ( so no warning about charges, no need for you to be home ) , but subsequently a test shows no detectable fault , but you are still having a BNR problem, hence the warning and need for you to be at home on the day of the fault visit.
You wouldn't be having a significantly different customer experience if you were a customer of any of the other mainstream providers, as they all follow the same process when asked to arrange an Openreach visit