SGH-I257 Samsung S4 mini
I bought an AT&T sim locked S4 Mini smartphone,
I requested an unlock code and my request got accepted, but the device is showing that the code is wrong ("Unlocking is unsuccessful").
I've done some searches on Google, and I found some solutions that say I should enter the Unfreeze code (MCK) first, and then the received unlock code (NCK).
How do I get the MCK code ? AT&T only sent my the NCK code but the unlock process failed
Note : my phone is NOT rooted, and has the official firmware.
I hope I get some useful answers. Thanks