By default all subdomains, created through the CPanel don't have 'www'.
If you need access your subdomain trough www.subdomain.yourdomain.com (not only through subdomain.yourdomain.com) you need to do some manipulation.

There are two ways to make it possible on CPanel.

1. Complicated.
Create subdomain as additional separate account. In this case your subdomain will be availble through 'www' and gets its own control panel for email, ftp, subdomains and other features. But to do this you need access to the WHM (reseller control panel).

2. Simple.
Create subdomain trough CPanel (ACCOUNT SETTINGS -> SUBDOMAINS)
and Email us on support@hostony.com and point name of your subdomain.
That is all.
We will add necessary DNS record and change Apache config to make your subdomains accessable trough 'www'.