If you want to switch back from your custom domain to your free subdomain, you can do that. To do that, you’ll need the following:
- Have the subdomain you want and assigned to the account. It’s easiest to use the account where the custom domain was assigned to.
- Make sure that the website files are located in the htdocs folder of your website. That used to be the case, but then you removed and re-added the domain name, causing it to be linked to a different folder. Fortunately, you can just move the files: How to move a website to a different directory
- Update your WordPress website URL to use your free subdomain. This is the most important part, and probably the reason why you’re being redirected to your expired domain name. The easiest way to change it is through the WordPress admin area, but there are other ways to change it if you don’t have access: Migrating WordPress – Advanced Administration Handbook | Developer.WordPress.org