It is registered.
Always refresh the page a couple of times, because Freenom’s WHOIS can erroneously give that error.
I also receive the same message (This domain name is not registered, we can register this domain name for you.) on the Control Panel (by trying to add Addon and Parked Domain).
I would say to try creating a new hosting account, but when I tried creating one on the Client Area:
I could be wrong, but I don’t think you are able to create an account (or add to an existing one) with the domains you want.