Hello guys after trying everything that i found in google i decided to take the matter in my own hands 
So facebook notifications have been a serious problem for many users for a long time,and this is how i fixed it !
Go to Settings -> General,scroll to the bottom -> Reset. Click on Reset All Settings (this will reset all your settings and your phone will switch off.
When switch on your phone,go to Settings -> Facebook -> click on your facebook account name -> Delete account.
Your notifications should be working now.Test them and if they do,you can sign in your account again.
P.S. This solution has worked with 4 people by now (iPhone 4s,iPhone 5)
P.S.2 I don't know if there is any connection,but i do not have Facebook Messenger installed.
Hope i have helped !
So facebook notifications have been a serious problem for many users for a long time,and this is how i fixed it !
Go to Settings -> General,scroll to the bottom -> Reset. Click on Reset All Settings (this will reset all your settings and your phone will switch off.
When switch on your phone,go to Settings -> Facebook -> click on your facebook account name -> Delete account.
Your notifications should be working now.Test them and if they do,you can sign in your account again.
P.S. This solution has worked with 4 people by now (iPhone 4s,iPhone 5)
P.S.2 I don't know if there is any connection,but i do not have Facebook Messenger installed.
Hope i have helped !