Received 5 consecutive calls from different numbers within the space of 1.5 hours.
The first 4 were silent hangups which I added to barred numbers.
The last one I answered by shouting "HELLO!!!" into the phone, which triggered(?) a recorded message, "Your BT broadband service will be disconnected ... (words to that effect)" - number barred
Thing is, I wonder if you need to make a verbal response in order to trigger a recorded message?