Well, then your belief is wrong, because it is a subdomain.
Unfortunately, this s the only way out. Accept it and solve your issue, or ignore it and have your issue stay there.
In order to remove the subdomain, you’ll need to use the “Domains” tool in your client area. Then, with the very same tool, click the “Add Domain” button, and add your domain back.
Then you’ll have to move your website from the original htdocs into cel-ia.free.nf/htdocs.