[if_its_fixed_i_wil_break_it]

I have just unlocked my 9900 previously network locked to AT&T using a mep2 unlock code . Typed mepd all is unlocked put in my straight talk sim and gsm and the bars came up in the corner everything indicated that all was well. Then a few seconds later I get red SOS. I checked and network provider said AT&T again?? Someone who has been there done that or has any advice I'd appreciate it. Worst case scenario ill try and sell it but I'd rather just get it to work and give it to my son. Even if its just SMS and calling only. At this point data isn't important to me. This is my first post although I've been a troll here for years and appreciate you guys and your input to the site, someone please help me out. Lets get to work!

Ps. I have done battery pull hard reset and phone wipe.
Pss. By troll I mean read posts without being a registered member, so if I'm misusing any terms incorrectly please forgive me and be nice, I'm a lady.
Thanks everyone in advance