Why can't my Apple iPhone 5s sync with Facebook?

My friends and I have checked our phone settings both on Facebook and I phone settings and they are all set the same, yet my phone is the only one that will not sync with Facebook. I cannot play Candy Crush with my friends and it's very frustrating. I have followed the instructions given on the Candy Crush website to fix the problem but none of it works. I wind up losing all progress I've made and have to start the game over. I've lost all my progress and have had to start over I don't know how many times. I'm about tired of trying. I keep thinking there just HAS to be someone our there who knows how to fix this!! Does anyone know how to fix this problem? Thank you!