Stock(ish) Samsung Galaxy S4, Unable to Unlock?

Hey everyone, I've been searching for a while now and I just have no idea what's going on with this phone. My mom bought this phone off of Amazon and it was claimed to be unlocked. Upon inserting the sim card, there was no prompt for an unlock code however the phone could not find service. I tried entering in many APN's found on her carriers website and from other sources, nothing had worked. I then decided to do the same with my sim card (from a different carrier) and still, nothing.

I then tried to access the service menu, in attempt to unlock the device that way. NONE of the codes/methods worked (for anything). I couldn't even find the "carriers" folder in /efs, no apk's, nothing. I tried to install various apps that would open/prompt the menu, however none of them could. I truly don't know what to do, I cannot take it to a place to get an unlock code because there is no prompt to even unlock the device in the first place. Any help is appreciated, I'm usually fine with rooting/unlocking my devices (I did my Nexus 5 and S4 SGH-I337M without a problem) however this one truly has me stumped. Thanks :)

Guides referenced:
[HOWTO] Enable Hidden Menus for Verizon Galaxy S4 - http://forum.xda-developers.com/show....php?t=2303905
Unlock Galaxy s4 sch-i545 - http://forum.xda-developers.com/show....php?t=2568274

Device Info:
Samsung Galaxy S4 (SCH-I545PP)
Android 5.0.1
Rooted (why I included the "ish" part)
Stock ROM