can not logg off icloud because Find iphone needs password to old nonexcisting apple-id account

A while ago i changed the email adress to my AppleID and also changed the password. The account is working perfectly fine both in itunes and applestore, but the phone constantly want me to logg on to my Icloud account with my old email adress. even though when i type in the adress to get a password i am told the account does not excist. The thing is that on my Ipad i just logged off iclud and then logged inn with my ned email-adress and password. This is not possible on my iphone because the app Find my iphone needs the password to my old account to be switched off. How do i delete the acount and logg on with the new one? Can anyone help me? Thank you :-)