I think you are missing my point. The fact is that BT customers are under no obligation to supply you or anyone else free internet access. BT run and manage paid for hotspots, now, if you were paying a separate monthly fee to use those access points then you would have grounds for complaint. As it stands you have none.
As has already been pointed out to you. BTWifi is a signal that is broadcast by BT broadband customers' Homehubs and not by BT. The customer is under no obligation to broadcast this signal nor maintain or use the Homehub so that the signal is broadcast. BT can not do anything if a BT customer's Homehub is not broadcasting the signal or if the customer decides to switch off the Homehub or use another router.
There are paid for BTWifi hotspots which are maintained by BT and as a BT broadbad customer you get free access to them.
If it was one of those hotspots that you wanted to connect to and it did not work you could report that to BT and they would be able to do something about it.
BT will do nothing to assist you, other than check your password is correct, if you can not connect to BTWifi home users hotspots.
You could try logging onto BTWifi via a web browser rather than using the app incase it is a problem with the app.