How Facebook helps an abusive ex-partner find out your new identity, even after they’ve been blocked
And Facebook have no intention of fixing this. They don’t consider it a bug.
Clearly Facebook users who are using the block functionality in the scenario given above are not properly protecting themselves. If you worry that someone you were previously connected with via the site might be stalking you, the best advice might be to delete your account and start a brand new one under your different name.
That is if you want to remain on Facebook at all…