Fixed and nope, it was a stupid configuration i have done with world guard that made the region grifiable. But, i fixed it and I learned that I don't have to put that configuration again.
Sorry for my stupidness and thanks Rice for the help!
PD: all the griefers have been found and have been globally perm banned from the Happy Hunger Games Network. Also, their chests have been cleared and the diamonds and missing MOD books have been found out. If anyone is wandering, the main griefer was ZombieManiac172, he was perm banned, his faction has been disbanded and all his chests have been cleared. justice was made :,)