How to resolve sim network unlock unsuccessful for samsung devices ?
this is because the phone was tried to unlock with free method and messed up the security zone. however dont worry try like this and it will be unlocked..
put different network sim card and power on the phone then when it asking for sim network unlock pin,
dismiss it then -
a. Go to the Dial pad and dial *#197328640#
b. Please click on number  UMTS >  Debugging screen > Phone Control >  NETWORK LOCK
c. You will see 3 options
d. Please click on number  Perso Sha256 INFO, the screen will change slightly
e. Please hit the MENU button then when the menu pops up please carefully hit BACK to return to the previous screen
f. Please click on number  Perso Sha256 ON, the screen will change again to a one line message
g. Restart the phone on the screen by holding the power button and click RESTART
h. When the phone prompts for sim network unlock pin first type "NCK" press unlock if shows error then type "DEFREEZE" and press
unlock it will show error then again type "NCK" and phone will be unlocked now.