My reply is for rhytha although perhaps a mod would prefer to move his/her post to its own thread.
If I understand you right:
- You are trying to register a new domain rather than add it to cPanel.
- You are trying to register your new domain via your hosting company rather than directly with a registrar like enom, godaddy or namecheap.
- You have been unable to register your domain name through your host's package.
If I have understood what you have said, then I think you need to contact your host and tell them you're unable to register a domain using their package and ask them to fix it. If they can't/won't fix it, then register the domain with someone like godaddy.