SIM swapping (otherwise known as SIM hijacking, SIM splitting, or SIM jacking) is a type of account takeover (ATO) fraud through which attackers get control of a target’s phone numbers. This is done by convincing their mobile phone service providers to swap the phone number to an attacker-controlled SIM card either with the help of a bribed employee or by using social engineering. The FTC lists the following measures you can take to protect against a SIM card swap attack: Don t reply to calls, emails, or text messages that request personal information.
Source: https://www.bleepingcomputer.com/news/security/ftc-issues-guidance-on-protecting-against-sim-swap-attacks/