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.
You could try turning on Do Not Disturb for all numbers, all the time. The calls and texts will technically still happen but you won’t be notified of them. You may be able to avoid voicemails if you never set it up. You’ll see all your texts if you ever open the app although you may be able to disable or remove it. (YMMV based on your particular phone.)