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.
AFAIK this is not possible for a working number. Failed dial tone and “text message not delivered” are handled on the carrier level, if you block a number then they’ll just get a “busy” tone when calling and nothing when texting. You can’t blanket reject everything while retaining data, unless you disconnect from cellular and only use WiFi.
Yet Another Call Blocker does block all calls, that is my phone never rings, and I never see any notification of a call.
Yeah but like I said, anyone who calls you will just hear the “busy” tone or direct to voicemail. They won’t get the “invalid number” tone like OP wants.
That’s doing that locally on your device, not on the carrier network. It’s definitely a good solution for this problem though.