Q: iphone 5s straight talk activation outside USA

Dear friends,

i bought iphone 5s from Walmart on Straight Talk. then brought it to Bangladesh without activating it. now, i cant activate it. of course straight talk is unavailable in Bangladesh. so what are my options? i have tried to activate it without sim. i can get to home screen but it doesnt accept any sim cards. factory unlock enquiries suggest that the phone is already unlocked. so i am confused.

have any of you faced similar issues? how can i activate this phone so it takes local bangladeshi sim cards?

thanks in advance.