you're asking this in completely the wrong way.
Without telling and showing us all the details there is absolutely no way anyone can help you.
you need to provide:
-link to the game
-source code to see how things function
-the method being used for the cheating results (will be an exploit in the code)
Even if you did provide all that, there's still a very high likelyhood that no one here will be able to help as software development is *not* a focus here
furthermore there is no 100% way to be sure the program is hack proof. You can fix the current method, but there's almost always workarounds and alternate exploits to be discovered
This fact compounds as the software becomes larger and more advanced.
you're better off going to software development communities and discussing the situation with them. You will need to be fluent in the language(s) used in order to discuss it with them as well, otherwise whoever is in charge of the actual coding needs to handle it