Double problem on Apple Mail: yahoo account and keychain!! HELP!

Hi everyone I know that this is an old problem with Mac to set up a basic account Yahoo (infact I checked on google and youtube how to sync yahoo account on Apple Mail) but my situation get more complicated, now I'll explain you what happened:

I had the Yahoo account on my Apple Mail (on my Macbook Pro) working perfectly till 2 days ago till I had for security reason to chage my password on my yahoo account, and so I did it.

When after I went to my Mail, obviously, the app asked me for the yahoo password (because Mail coudn't get the access to my Yahoo account) so I typed the New Yahoo Password and checked the box "Remember this password in the keychain" but Yahoo mail kept asking me for the password again and again (old Apple Mail problem); therefore I went to the Keychain Access and I correct the voice imap.mail.yahoo.com and typed in the New Yahoo Password, saved, and before close the Keychain Access checked if the voice login.yahoo.com was ok and close the keychain app.

I opened again the Apple Mail and all my mail accounts were sync perfectly except for the Yahoo one, that kept asking me for the password so I deleted the account and after try it to set on Apple Mail a new one.

I follow a lot of tutorial to set up a yahoo account on Mail but at the end the result is always the same, the Yahoo account doesn't sync and Mail keep asking me the password again and again I tryed to reinsert all the password but doesn't help, I also deleted all old yahoo voices on the Keychain and did new ones but nothing happen... this is ****** me off a lot!

Hope someone can found the trick.

Sorry for my English

Thanks

enrico86