Start punishing him...make him do chores..have him right sentences...take things away, like toys, games, tv...
It doesn't sound like whatever it is you are doing, is working. So mix it up. Try just the opposite. If you've been yelling, sing. If you've been punishing, tickle. Think up creative rewards instead of angry consequences and see if he goes for compliments. Try ANYTHING else besides what you've been doing --- think of it this way, he is immune to those other ways.