Default No Sim Card - But phone shows network bars

Hi , on my note n7105 my phone suddenly stopped recognizing my sim. It keeps saying 'No Sim, insert sim card" despite the sim card working ( i tested it on another phone)

My phone shows network bars despite it saying i have no sim card inserted. When i have remove the sim card, my phone still says i have network signal. My phone is rooted but running stock rom 4.3 . I have tried factory reset and it is still not working.

How could this happen suddenly? I have not dropped my phone recently or anything.