Find or create another interest, go volunteer for something or take a class, etc. You are not "addicted" to the internet, you are just not looking for other activities or are on the internet because it is easy. What would you like to do/be/try? Do something that will move you further in that direction.

If you don't want to spend as much time on Facebook, delete all your games and all your "friends" who you do not know in person and send all your friends a message that you are not going to be on very much anymore (that's what I did). I found a health site that was more helpful to me and had the same interaction opportunities as Facebook but about subjects more "useful" to me.

Take an online course from your local community college or university. "Working" online does not feel like you are wasting time as just wandering around, surfing or playing on Facebook can.