Technically they can, practically they can’t. Your number is your property and you’re allowed to switch between carriers as per your desire as often as you like. No carrier can force you to stay with them regardless of whatever the situation is, so they’ve made it super easy to switch in case you want to. This easiness have made the job of hackers much easier where they’re able to do it without your consent. We’ve tried multiple things from instructing carriers to put notes forbidding port out to putting pin numbers, but none of them will prevent a sim-hack because of how the system works. It’s a pull approach vs push where a carrier receives a request that a user is porting-out and as long as the information matches, it’s automatically approved. You’ll be surprised that the only information required is Account # & your telephone number for a port-out which is very easily available. In a rare case of Pin number, that can also be obtained super easy. So once the hacker have the information, it’ll only take him couple of min to take over your number and then start misusing it for it’s ill-intention.