[lewisjoe]

There is an even more easier way to hack. When I got my new phone number, I found out that number was recycled and the previous owner's facebook account was now linked with mine.

From there it was just a few mins before the account came to my control (I was experimenting and seriously believed it wont work). I reached out to the owner through email and informed them to unlink their phone numbers.

I reached out to Facebook through their bug bounty and explained the case. They simply replied they couldn't do anything and it's the phone number provider's fault to recycle.

[WhyNotHugo]

Tying accounts to phone numbers is extremely dumb. People change numbers. Numbers get reused. Also, for many companies/regions, if you lose your SIM, you lose the number (e.g.: if you don't have a contract but just a pre-paid SIM).