Permalink, Parent and Sub Category

I have a strange problem, where when I click on the permalink, parent and sun category of the post I get 404 error.

What have I done wrong, how do I solve this problem?

I also wanted some clarification and guidance on how to use parent and sub categories.

I have created a parent Category Movies and then created a sub category Hindi Movies. I then created a post and filed under sub category Hindi Movies but for some reason the post lists that the post is filed under both parent and sub category. Is this how it is suppose to work? I though the post wil only appear in the sub-category.

I have the following set-up under admin->settings->permalinks

/%category%/%postname%/

Here is the url of the site for reference:

https://i31.us/

Many thanks for help.