First thing to check is that your phone bill is paid for the month so you can rule out your service being cut off, also check to see if mobile data is turned on in the notification shade. Second thing you can do it is to try out someone else's SIM card (preferably someone you know and has the same carrier as you if your phone isnt unlocked) to rule out your SIM being damaged or defective. If it still isn't able to read the SIM or says no data I would take it to a shop to get checked out and examined for any liquid damage. If there's no liquid damage or physical damage then I would contact Samsung to check and see if you're still under warranty and if so I would get the phone exchanged. If your phone was purchased through your carrier and you pay for insurance every month I would reach out to them as well.