I Need a Good Punishment for my Son?

Think about how petty you're being. You're mad because your son is cheating at an online game, so you want to ground him? It's better to let him learn for himself that there are no shortcuts because he will eventually be caught/banned. Don't worry, he'll get what's coming to him... but if you try to punish him for it directly or do something else you'll just look like a jealous/petty parent. It's an important life lesson that hard work is rewarded and that cheating never pays off, and it's better that he learns it now than for him to get the message that "cheating works, but my parents just don't get it and want to punish me for no reason."