I used to work at a cell phone company. One day I needed to change my SIM card so I call up the help desk : "Hi I have a new SIM card, can you please activate

I used to work at a cell phone company. One day I needed to change my SIM card so I call up the help desk : "Hi I have a new SIM card, can you please activate it? — Sure what's your number and IMSI? — My number is ..., the IMSI is ... — OK done" And so, just like that, I took over someone else's phone number. Not on purpose, but the guy made a mistake punching in my number, didn't verify my identity, and ended up assigning someone else's phone number to my SIM card. I called the guy back after realizing that I wasn't getting calls and that the people I called thought I now had a new number. Granted it was a while ago but the experience gave me a very low opinion of SMS for 2FA.