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?

closed as off-topic by Xander, Tobi Nary, AJ Henderson, Steve, Bacon Brad Aug 30 '17 at 21:34

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about Information security within the scope defined in the help center." – Xander, Tobi Nary, AJ Henderson, Steve, Bacon Brad
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 3
    Probably they use a service like Whatsapp or similar that required the new phone number and shared that to the existing contacts? – nulldev Aug 17 '17 at 7:58
  • In which country this is in, and is the new number with a prepaid SIM-Card or with a contract? – nulldev Aug 17 '17 at 8:00
  • Some providers, at least in my country, have an explicit anti-stalking service where they provide a new number for exactly this reason. Does such a service exist with someones provider? Did you try it? – nulldev Aug 17 '17 at 8:01
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    Others have already asked some questions, but more broadly speaking: please provide more details. For example, are there any applications installed on the phone where the SIM (with the new number) was used? Was the number used for anything, e.g. calling a friend or a corporation? Did you rule out things like: the spouse works at a carrier or has friends there, or works for law enforcement or has friends there? Etc. That said, this is quite a specific question, which might not be a good fit for the site. There are already 2 close votes, but I'd still encourage improving the question. – Luc Aug 17 '17 at 15:40
  • WhatsApp displays one's phone number. If a person is active in WhatsApp groups, this can give away the new phone number. All that the attacker has to do, is be a lurker in at least one of the target's WhatsApp groups. – S.L. Barth Aug 30 '17 at 8:43

The service provider can sometimes retain that same number, and when a person attempts calling it again the service provider may redirect the call to the new number, as they would assume the person calling is trying to get in contact with the person whom changed their number.

A precaution would to be to contact the service provider (assuming you are a legal figure) and tell them to disallow any further phone number changes.

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