ZenFone 2 ze551ml [z00a] bootloader does not unlock (please help)

I tried every possible way to unlock my boot loader.
I used various apps given by xda developers .....
I tried the official app to unlock the boot loader.
Flashed a rooted ZenFone system [downloaded from a link provided by xda]and then write the code to unlock bootloader:-

[adb shell]
[SU]
[getprop ro.isn > /factory/asuskey]
[Reboot bootloader]

Still it did not work......
I have been working on this since a month now and even now I can't figure out what the problem is .
please help me find solution.
Should I reinstall the fastboot mode ?
Pls help

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