f you believe cPanel or WHM displays incorrect disk space, there may be 2 reasons:
1. Your cPanel displays you have only 200 MB space, but you have ordered reseller package with more resources. It means cPanel displays your main package information only (reseller package has 200 MB assigned by default). To assign more space, please create a new package via WHM, then select "Upgrade/Downgrade an Account" and assign your new package to reseller account.
2. When creating a new account, WHM displays you have less free resources (disk space and bandwidth) that you should have. It's because overselling is disabled to make sure your accounts are running at top performance. Let's say you have reseller package with 2000 MB space and created a new account. Account has 1000 MB package assigned, but only 500 MB space is used. When you will create a new account, WHM will display you have only 1000 MB free space. It's done to make sure your accounts will not exceed assigned space and you will never run out of your resources. WHM calculates disk usage by assigned packages. So if you have lots of small accounts (which use 100 MB space for example), you need to create small packages as well.