Dear Samsung member,
Greetings from Samsung customer support.
We acknowledge your query and apologize for the inconvenience caused to you and will surely assist you regarding the same and please follow the easy troubleshooting steps which might help to solve the issue.
1. Reinsert the SIM card.
2. Check the existing SIM card with another phone, if the problem persists, then there will be an issue with the SIM card. After testing, if find out is sim card is faulty please refer to the service network provider.
3. Check your existing phone with a new SIM Card. If the existing phone's SIM slot may be faulty, please continue to refer to the below steps. When a SIM card is cannot be detected, there are other possible causes:
1. SIM card is not inserted properly.
2. Loose SIM card slot will be caused the card to lose the connection with the reader of the device. You can try to apply some pressure to the slot check again if the slot holds the SIM properly.
In case the issue still occurs. Please register your concern in Samsung Members Application (Open Samsung Members Application > Support> Tap on error report > Type your query > Send).
Thank you for writing to Samsung.
Samsung Customer Support