Default [Q] Sim Card Error

I have literally been searching this site for hours trying to find an answer but nobody goes into much depth about this problem. My i9500 cannot detect my sim card at all. I have replaced my Sim Card Tray twice since receiving the "sim card error please restart phone" notification because it didn't seem to fix the problem the first time i replaced the tray and I wanted to be sure it wasn't a bad tra. I have tested the Sim Card in 3 other phones and it definitely works so I don't understand what else it could be. Please help me guys. I need this phone for work and I can't afford to upgrade right now.