Samsung Galaxy S3 from AT&T, stuck on Edge after unlocking..what do I do?

[AC Question]

samsung galaxy s3 from atat, stuck on edge after unlocking....

I bought an unlocked samsung s3 online... but its stuck on EDGE cant get 3G or 4G or LTE on it.... there also is no option to change it at the network settings even after factory reset,... what do I do ??