I found this app for Mac (edit: forgot link http://selfcontrolapp.com), which unblocks it for a certain time and you can't take it back no matter what (which is exactly what I need). But as long as I still have access on my iPad and phone, it'll be useless!
Good luck to you!
This works best if your problem is mindless habit. If you lack willpower, you're better off with something more aggressive like FocusMe or Cold Turkey.