Can't get lock screen back.

[AC Question]

I used to access my phone (Samsung galaxy NOTE 4, recent andriod version 6.0.1, almost a year old phone), using finger print but also had a backup password .
Today, I had to change my backup password but as soon as I did, following happened:- (READ CAREFULLY TO UNDERSTAND)
1- I lost all the security from my lock screen and I can only swipe to open my phone.
2-In order to change my lock screen back to finger print, pin or any other option ,I go to 'SCREEN LOCK' option found in settings. But in order to change the type of screen lock (finger print,pin etc) I have to enter my password to access the options.
3- BUT MY PHONE IS NOT ACCEPTING MY PASSWORD AND KEEPS SAYING , SORRY INCORRECT PASSWORD although i am entering correct password.

HERE'S WHAT I DID TO SOLVE THIS PROBLEM:-
1- my finger print is stored (but not working on my lock screen), and i can use it to change my backup password. I DID THAT.CHANGED MY BACKUP PASSWORD SEVERAL times but nothing happens. STILL CAN'T GO TO SCREEN LOCK SETTINGS TO CHANGE SCREEN LOCK FROM SWIPE TO ANY OTHER.
2-tried all possible methods found online i.e cache deletion, ADM, samsung mobile recovery ,changing the screen time out, credentials ,everything.
helppp