Can't make call to 2 specific numbers (that were fine in past). 'Call Failed'

My phone is fine with most numbers, but I have two contacts/numbers - my wife and my sister (so the numbers I've previously called most frequently) that give a 'call failed' message and do not connect. I can't send a text to my wife either.

My wife is on EE, my sister on BT (so both same network in the UK).

It makes not difference if it's a mobile call or wifi calling

I can receive calls from them.

They are not in my blocked callers list.

I've tried completely deleting the contacts and reentering them manually.

I've cleared my recent calls list.

I've been through an hour of checks with EE on the phone, reset my carrier settings, rebooted the phone. My phone isn't IMEI blocked and I'm told everything appears fine with my account.

I'm on an iPhone 15 pro.