Property 'levelCompleted' not found on object of type 'id'

Here's my model class LevelInformationModel.

     @interface LevelInformationModel : NSObject

     @property NSInteger levelCompleted;
     +(id)sharedModel;

     @end


     #import "LevelInformationModel.h"

     @implementation LevelInformationModel

     @synthesize levelCompleted;

     /* Return singleton model */
     + (id)sharedModel {
         static LevelInformationModel *sharedModel = nil;
         static dispatch_once_t onceToken;
         dispatch_once(&onceToken, ^{
             sharedModel = [[self alloc] init];
         });
         return sharedModel;
     }

     - (id)init {
        self = [super init];
        if (self) {
            self.levelCompleted = 0;
        }
        return self;
     }

     @end

And here's how I'm using it all (in GameViewController class). I have imported LevelInformationModel.h already.

     NSInteger currentLevel = [LevelInformationModel sharedModel].levelCompleted;

But above the levelCompleted property is the error Property 'levelCompleted not found on type 'id'`. Any thoughts would be great.