just keep at what you're doing... it's not possible to spot reduce fat from any area, especially not your abs. genetically your body has a predisposition to store fat the most in three places: your glutes, thighs and abdominal region. all you can do is eat right, work hard, and eventually it'll go away.
that being said, the abs are the hardest place to get rid of fat (for some reason...

), and the lower your body fat gets, the more it's gonna wanna hang onto it. towards the end, it's gonna seem like you'll never get rid of it, but it'll happen. just stick to your guns