Our nameservers are set up so that any unknown (sub)domain is redirected to a parking page. It’s not possible to change this for your own (sub)domains, other than assigning the subdomains to your hosting account.
The only way to remove these parking pages for your domain name is to move it to nameservers where you get full DNS controls. Premium hosting comes with full DNS management. But if you’re able to manage your own DNS records, you could also move your own domain to separate nameservers.