It is not just a generic answer, I'm afraid. It is an accurate one.
The WordPress.com user account that you are posting from is not the owner of the kathy-fish.com domain registration. This is why you are unable to to renew it when you click the link. If you were logged into the WordPress.com user account that owned the domain registration you would be able to renew it.
The domain name that WordPress is telling me is about to expire has been switched over to another domain server as I switched the site to WordPress.org.
I'm afraid this is only part of the story. You changed the domain's nameservers to point to your new webhost. But the domain itself is still registered through WordPress.com, which is why you are being sent the renewal emails.
You have a second WordPress.com user account and THAT account is the owner of the domain. You must log into that account in order to renew the domain. Can you look at the email address that the notifications are being sent to? To be clear, this may be different than the address where they are arriving. So please look at the actual email to/from/subject lines to be sure. If it is a different email address than you are using to log into the account you are posting from, please try running it through the password recovery system:
If that does not work, let me know and we will see what else we can try. \