Is there a way to unlock the Galaxy Light to use on another Carrier manualy?

I bought a sgh-t399n at a garage sale recently and quickly rooted the phone and installed TWRP Recovery and CM12 on it. I called Metro and T-Mobile ( After flashing their firmware) for the unlock code but of course they refused to give it to me. So i tried 2 or 3 different unlock by IMEI websites as well as every single unlock app and software I could find while running logcat. The best lead I've gotten was the S.G.S. Unlock Tool app. It says it found the code but the results are null. In the logcat the system denies permission saying that the app was sending request as -2 when it was 0 and that it needed "android.permission.INTERACT_ACROSS_USERS_FULL " to accsess the info. Now I'm not a Dev by any definition of the term, nor am I any kind of hacker but I have learned a good bit from these forums over the last couple of years and my gut tells me this can be done with a little patients and some help from the good folks at XDA. Any imput on the subject is greatly appreciated.