Good day sir,
from my knowledge users of third party software can be removed by restricting their access to the game because violation of the terms of service that players have agreed on.
Players can also use the report system implemented in the Metin2 Version 25.1 in case of suspicious behavior as GameMasters cannot be reached.
While the possibility of e-mail assistance has been deactivated with Metin2 Version 25.1 the usage of the ticket system is still active.
Cheating is a known big problem to the quality of Metin2 and is to be handled by the publishers and developers of Metin2, but the nature of the game makes it hard to completly prevent.
As of today the introduction of access-based servers like Tigerghost in 2020 have become a solid option for the playerbase that prefer to experience the game with less the impact of third party applications on the game.
"Tiger ghost: less cheaters, more events (need invite code)
Ruby/Emerald: Even less cheaters, more events (paid sub: 5$? A month) ... "
Conclusion:
Due to the old age of the game and technological restrictions it is unlikely to completly prevent third party usage but the game is very much playable with some small adjustments in terms of gameplay.