[Q] i9500 not recognizing SIM card topic

So yesterday I was messing around with my i9500 that I've upgraded to Lollipop.. due to rooting issues, I decided to downgrade back to KitKat (flashing the stock rom using Odin)

however, as I fixed all the rooting issues, I've encountered a new one - my sim card seems to be no longer functioning (even though it is inserted, the phone claims that no sim is inserted

any tips? I rely on data and phone calling as a large part of my phone ._.

help!