@nikolal when I did it, which was over a year ago, I think the period was two weeks and if you tried logging in again in the period, it would undo it. So first I removed the Facebook app from all devices and cleared cookies everywhere. Then I logged in once, changed my password, disabled the account, logged out, cleared cookies again, and set a reminder for sometime after the period to try logging in to ensure it was deleted. Not sure if they have made it even harder now.