help with WorldGuard and permissions

Hey, ive been searching a lot on the internet but i didnt find anything, so ive decided to post here. The problem is that i want to let players mine only a specified material(coal ore) inside a region. I tried using modifyworld permissions from essentials but it didn't work, i also tried to enable the worldguard permission system and adding the "worldguard.build.block.remove.<material>" (<material> being "coal_ore") permission to the default group, It didn't work either. I allowed the block-break flag with the wg permission system but it didn't work. I left the region. Didn't work. then i added the permission "worldguard.build.block.*" to see if it was a problem with the permission, but then i could break and place every block. So i removed that permission again and added "worldguard.build.block.remove.*" and surprisingly it didn't allow me to break blocks, then i added "worldguard.build.block.place.*" and i couldn't place blocks either!!!! So i think there is a problem with the permissions inside "worldguard.buid.block", can someone help me PLEASE!!!!!!

Also i can't add more plugins because im on Minehut that only allows you use 12 plugins in their free plan. Im using Skript so maybe i can solve this problem using it??? Idk