[Q] At&t S4 simunlock help topic

Hi all
I am newbie to the android world, i was gifted an at&t. S4 i337 model for new year. It was purchased as an unlocked device so it can work in india, but it wasnt,when i load my indian sim ,s4 always prompts with simunlock code.

I read lot of the xda thread to overcome this , intially s4 was in 4.2.2 MF3 build, i was able to root the device but i wasnt able to unlock for international band. So i updated to 4.3 using the thread "http://forum.xda-developers.com/showthread.php?t=2573080" since most of the reviews had positive feedback for unlocking. My software version got updated to 4.3 mk2 build But to my notice after this s4 loads with custom unlocked padlock symbol and rooting dosent work, it always fails when i run the supersu app in disabling knox step.

I followed every step as it said in the thread ,but failed every single time, the thread says it will work only with stock rom, since it boots with custom is this the reason for failure. How can i recover from this. Ur help will be appreciated, i have my s4 unused for past 1 month because of this.

Thanks