Blocking subdomains from cpanel

Hi all. I have the main domain. it is xyz.com. when adding a new domain to host a new website abc.com, a subdomain is created automatically abc.xyz.com. i can see entire website on abc.com but also can see website abc.xyz.com which i dont want. how do i disable that ? i dont whm access, only cpanel access. i have 100 domains to be hosted and i dont want websites to get accessed from subdomains too. . How do I prevent the subdomains of the main cpanel domain from showing web sites?