Disk usage problem: WHM is showing incorrect disk usage details and I cannot also change the disk quota via WHM. (Use disk space)
The problem happens when the disk quota file get corrupted on server. You can run the following command while logged into the server through SSH as the root user.
/scripts/fixquotas --force
In that case, a quick reboot of the server will help to solve the problem. You may restart server via Power Panel.