My sim stoped working

Power off the phone and eject, then replace the SIM card. Power on the phone. If you have cellular signal bars on the phone and still cannot send or receive calls (or texts) then confer with your Cellular carrier to ensure there is no issue on their end and your account is in good order.

If all is in order with your carrier, then book an appointment with the nearest Apple store, or Apple Authorized Reseller for their perspective on what may be wrong.