Praise be to Allah.
If the game is free of anything that is contrary to Islamic teachings, there is nothing wrong with playing it, and there is nothing wrong with buying crypto currency in the game with real money. This is akin to paying fees to use the game or for extra features in the game. This has been discussed previously in the answer to question no. 199031 .
It is not permissible to hack games in order to obtain crypto currency instead of paying for it, because that comes under the heading of consuming people’s wealth unlawfully. It is also a transgression against intellectual property, patents and copyright, which are protected under Islamic teachings.
The Islamic Fiqh Council issued a statement having to do with intellectual property rights, in which it says:
Thirdly: copyright, patents and so on are protected under Islamic law; their owners have the right to dispose of them and no one should transgress against them.
End quote from Majallat al-Majma‘ (vol. 3, p. 2267).
The one who has cheated and did not pay money must repent to Allah, may He be exalted, and get in touch with the makers of the game to ask for their forgiveness. If they insist that he pays what he did not pay before, then he must do that.
There is no differentiation in that regard between one who was unaware of the prohibition and one who was aware of it, but the one who was unaware of it has not sinned thereby.
And Allah knows best.