'A sim-swap scam happens when a criminal obtains enough information to pose as you (Facebook!) and uses it to trick your mobile network provider into transferring your phone number to a sim card in their possession.
Gaining control of your mobile number allows a fraudster to receive all calls and texts intended for you – including the one-time security passcodes for online banking. It also allows them to intervene if we try to contact you to warn you about suspicious activity on your account.
If you ever notice anything unusual such as sudden changes in service or unusual messages from your provider, call them immediately using a trusted number from their website to check there is nothing untoward happening. The quicker you react, the quicker you can stop them in their tracks!'