Not just locally on the device! There must be an error when calling or texting the number.
Data must work for internet for Signal, VoIP, etc.
This is for a UK PAYG SIM.
There should be no way for anyone to demand my number, or for me to leak it, or doing so should be irrelevant as it does not work.
I don’t think so. As providers assign a number to each subscriber, like even an Apple Watch technically has its own number.
So the issue is the “way for anyone to demand my number “
Oh. Perhaps a hotspot; and tether to it. And use WiFi wherever you can otherwise? “They” could demand your number but it couldn’t ring you.