SIM swap fraud (also known as SIM hijacking) allows scammers to take control of a target’s phone number via social engineering or by bribing mobile operator employees to port it to a SIM controlled by the fraudster. Europol has also shared measures you can take to block SIM hijackers from stealing your credentials and locking you out of your accounts. The FBI has issued a SIM swapping alert with guidance on defending against such attacks following an increase in the number of SIM jacking attacks.
Source: https://www.bleepingcomputer.com/news/security/sim-hijackers-arrested-after-stealing-millions-from-us-celebrities/