Auto LogIn into face book

Hi , i connected my game with facebook API to share the result of the game, 2 months back it was working fine. when you click the button it ask for login then you logged into the face and sync your connection and share your result on Facebook.... and if you want to change your facebook account you remove the last account into the mobile account setting and add new one..... now the problem is when we add the account user id and password in the game it sync the account but when i off the game and remove my facebook account from the account setting and open my game , my previous account remain safe in the game and it share data with the last account we added before ........ what i am looking for is either a logout method properly or any other suggestion ... and i have used FB.Logout(); its not helping me out... here is my code

 public class MainMenu : MonoBehaviour {
 
     void Awake(){
         // Initialize FB SDK              
         enabled = false;                  
         FB.Init(SetInit); 
         }
 
 
     private void SetInit()                                                                       
     {                                                                                            
                                                                   
         enabled = true; // "enabled" is a property inherited from MonoBehaviour                  
     }                                                                                            
     
     void OnMouseDown()
     {
 
         if (!FB.IsLoggedIn) {
 
             FB.Login ("email,publish_actions", LoginCallback);  
 
         }
         else if (FB.IsLoggedIn) {
 //            OnLoggedIn();
         onBragClicked ();
                 }
     }
         
     void LoginCallback(FBResult result)                                                        
         {                                                                                          
 //            Util.Log("LoginCallback");                                                          
             
             if (FB.IsLoggedIn)                                                                     
             {                                                                                      
                 OnLoggedIn();                                                                      
             }                                                                                      
         }                                                                                          
         
         void OnLoggedIn()                                                                          
         {                                                                                          
 //        Util.Log("Logged in. ID: " + FB.UserId);
         FB.API("/me?fields=id,first_name,friends.limit(100).fields(first_name,id)", Facebook.HttpMethod.GET, APICallback);
 //        onBragClicked ();
         }
                                                                                                                              
     void APICallback(FBResult result)
     {
 //        Util.Log("APICallback");
         if (result.Error != null)
         {
             // Let's just try again
             FB.API("/me?fields=id,first_name,friends.limit(100).fields(first_name,id)", Facebook.HttpMethod.GET, APICallback);
             return;
 
         }
         
 
         onBragClicked();
     }
 
     private void onBragClicked()                                                                                                 
     {    
                                                                                                   
         FB.Feed(                                                                                                                 
                 linkCaption: "I just Found My Love Result." +
                     "Click to Check out your's",               
                 picture: "http://s16.postimg.org/r3fvqk5cl/jhj_3_2_2_2_2.jpg",                                                     
                 linkName: "LoveMeLoveMeNot",                                                                 
                 link:"http://www.brokenfloorstudios.com/"
                 );                                                                                                               
     } 
 
 }