Domain and IP confuser

Hello i have a sort of wierd problem.
I have a client who recent signed up for one of my shared hosting plans.
When they changed their dns servers to mine. they have registered one nameserver net on one of my nameservers and then com is on their nameserver.
Now the problem is net violates my TOS because its a gateway to their sphere cpanel for now i found out that they are shared or reseller hosting providers. they are trying using my servers to bounce folks into their site on their servers. which doesnt make sense too me especailly when they purcahsed a web host plan and not a reseller plan.
Two days ago i had emailed them and told them that i was going to suspend the account because breach in the TOS and gave them 48 hour to fix it. I never neard back from them. Tonight after 12AM. i followed through and suspended the account. The webpage that got suspended in whm was the com page. Now how did this happen and what can i do to shut down the TOS violating page? Besides cancelling the account because i have to wait 3 additional days as part of my own TOS Agreement.

In whm under list accounts, when you click the domain name dot net the bad page comes up and when you click the ip address the suspend page shows.
What is the cause of this and what do i do to close the offending page?