I've struggled with this, probably not to the extent you have, but enough that I recognize my decisions over the last two decades hurt myself mentally, socially, and career wise. I've tried to quit various things and of course eventually return to old habits (quitting does help though, I encourage everyone to at least try).

The only method that really works for me is to have other constructive things I genuinely want to do. It's easier to avoid picking up the phone or getting on the computer (breaking the habit) if I'm thinking about X instead. That can be a hobby, a project, or even better a friend, relative, child. I don't want to sound like I'm saying, "just do this one trick." I know it's not easy and everyone is different.

The children's book Frog and Toad Together has a story about willpower called "Cookies". It sums up my experience pretty well. If you do write a book about what works for you, consider making it a children's book: I've gotten more comfort and understanding from those than anything else.