Not sure if this is the place to ask this, but can't find a better SE section to ask on. I've been trying to help someone with securing someone's relocation from a domestic abuse case.
After changing this person's phone number, in under an hour, the spouse on the other end was able to continue calling that new number. As far as we know, we are the only people who know of the phone number change other than the service provider themselves. The phone is an iPhone 6. How would someone have gone about doing this, assuming no associated people have told the spouse the number and the spouse also did not have access/credentials to the service provider account that the number was associated with? And, what further precautions should be taken to prevent this from happening again with another phone number change?