Did you have a script? The script may be redirecting it depending on how it was configured.
Go to cPanel > Parked Domains and add the previous subdomain you had, this will make your website accessible by both your main domain and your old subdomain set as parked domains.
When you've done this you can login to your script administration panel and set it to work with the new subdomain.
Im not using a domain, only subdomains, as in .x10hosting.com. I don't think I can access cpanel if my subdomain won't even work. I also used the thing on x10.com where you login to change it.