It sounds as if you accidentally created two separate accounts. See if you have an old email that would have gone to the email address that published originally. Try to remember the password you used then. Might you, perhaps, have had an Amazon account before that you used to buy things, and then used it to publish your first books? And then created a separate publishing account too?
If you can figure out your two different accounts, you need to throw yourself on Amazon's mercy and explain what happened. They should be able to merge your accounts. Be polite and persistent, and reply to emails you receive rather than start a new chain. It may take a while to get resolved, and if you are able to figure out for sure what happened it will make it easier. Good luck!
I'm back. After my tirade a couple of days ago a Kindle agent emailed me offering help. He offered to merge my two accounts so I agreed. The accounts are now merged and everything is fixed. Sometimes a little venting goes a long way.
We are all of us at the mercy of the great god Amazon. Anyway for all of you suffering from missing books and duel accounts be persistent it's the only way. Now I will get on with some actual writing, my poor book will be thinking I've left it for a new younger more handsome one.
PS: I didn't just join Amazon on the 16 Feb as some one said, that registration date refers to when you first write on the forum. I joined Amazon way back in Feb 2011 and created the second account in June 2014.