Iphone 5c wont read any sim card HELP!!

I recently bought a USED Iphone 5c At&t carrier and the phone wasnt activated so i tried to activate it and every time I try to put a sim card inside it says "Insert a sim card" or "No sim" at the top left im connected to wifi and everything just it wont read the sim card I tried cleaning the sim card with alcohol with a cue tip GENTLY.

I called at&t and requested a unlock and they unlocked it but it still wont read the sim card the sim card is a Straight talk at&t sim card (non activated) (non used).

Why wont it work?

Ios 9.3.1