Not logging FTP bandwith

I'm with a huge problem. cPanel isnt logging FTP bandwith's usage. It's like, users are logging on the system using the ftp.mycompany.com domain and autenticating as their users and sending stuff.

I want to log users FTP usage to the bandwith. But how this can be done if they can logon using my main account ? I say... The account of my server's site ?

I would really apreciate a answer on this topic.

 

I'm using pro-ftpd. The problem is that users are acessing their account using the ftp domain from my main domain. How can I block this ? So they can use only the ftp.domain.com pof their own accounts ?