That's unclear. If it's created as you say, apparently it was created, and it should be accessible. it could be that you can't create such email addresses now (do you have a link to some source that says it can't be done), but old accounts should still be accessible.

All you can do: contact yahoo customer service. And don't fall for spammers that trick you into fake support, only to have you pay or install malware on your PC.