If showing diskusage 0 space in WHM as all accounts need to execute a fixquotas script.

Login into your Server by ssh login and run a below script,

/scripts/fixquotas

Installing Default Quota Databases......Done
Quota Mode: Linux
journaled quota support: kernel supports, user space tools supports (available)
Warning virtual file systems are mounted. Quotas may be counted as double
for users who are currently logged in. Please have jailshell users logout
before running quotacheck in the future!

Resetting quota for spacename  to 100 M
Reading package space_1000


Finally refresh the WHM panel on browser.