Comment by oretoz

There is an API available from many mobile operators called SIM Swap that can be called to find out if the SIM has been swapped. Often these calls are made by Banks to an aggregator (such as Telesign or Twilio) that finds out the mobile operator (e.g. Verizon or AT&T) that the customer belongs to and calls SIM Swap API on that operator. There is currently no universal app for that purpose but it can be developed. See CAMARA Project for latest specifications of this and many other APIs.