SSL Certificate Redirect?

Hi Experts, I have a site hosted with register.com and an SSL certificate installed through them as well. I set up a subdomain to be sub.xxx.com (or the sub folder in the root directory). The sub folder needs to be secure. when I go to

http://sub.xxx.com/ the correct index page appears, however when I go to

https://sub.xxx.com/ it displays an index page from another directory.

There customer support says i need to "change the redirect" but there is no redirect in place. I have tried creating one with the htaccess files but than it asks for a username and password when I go to the secure URL. If anyone has any suggestions/explanations it would be really helpful. Thanks.