Turn off your phone, get the sim card and reinsert again, and then restart your phone, if not work try to test it with other simcard, check also the simcard holder if something is blocking it, clean it if its dirty, if it not work have it for a cellphone repair
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Turn off your phone, get the sim card and reinsert again, and then restart your phone, if not work try to test it with other simcard, check also the simcard holder if something is blocking it, clean it if its dirty, if it not work have it for a cellphone repair