A couple of years ago i got a new phone which used mini sim instead of the micro sim that my older phone used. So i went to an AT&T store to get it and the rep asks for my name and my phone number and 5 minutes later comes back with a new sim saying it'll activate my noon the next day.

There was no authentication at all. Literally anyone could have walked in gave my name and phone no and would have gained access to my phone. I stopped using my phone for 2FA since then.