Block domains pointed to my server?

Hello to all! I noticed today 2 domains (totally unknown to me) pointed to my server (WHM Installation). As far as i can see these domains use different name servers than the one i have already configured with however the 'final' page is the default web page of cPanel hosted. I am wondering if i could block these unknown name servers and accept only the domains with the already configured ones or i could take under consideration something else in a matter of security. Thank you!