1. On the standby screen, click Applications-Settings-More Networks-Mobile Networks-Network Mode-Select only GSM.

2. If conditions permit, replace the SIM card for testing.

3. (Backup data: phone book, SMS, multimedia, etc. ), it is recommended to restore the factory settings.

4. It still can't be solved after the factory settings are restored. It is suggested to update the version of the mobile phone system to see if there is any improvement.

5. If the problem still exists, it is suggested to send the mobile phone to the nearest Samsung service center for testing and further processing.