Please follow the below mentioned steps in order to resolve the issue:-
> Perform the reset network settings (setting>>general management>>reset>>reset network setting).
>Ensure that network frequency of your device is selected on Auto-mode.
Menu>Settings> Connections>More Networks> Mobile Networks> Network Mode> Select Auto mode (GSM/WCDMA/LTE).
>Search for the Network Manually by the steps as mentioned:
Menu> Settings> Connections>More Networks> Mobile Networks> Network Operators> Select Manual Search.
>Insert different SIM card in your mobile and check if the issue is resolved or not.
> If still issue persists then we would suggest you to contact your service provider.
Team Samsung Members