Please try the below:
1. If the line is poor, hang up the phone and call again.
2. The network environment is poor, such as weak signal, unstable signal, etc., which cannot meet the requirements of a cable connection, try calling in a good network environment.
3. If there are high-speed moving objects such as a high-speed train or a highway nearby, try calling in a different environment.
4. If the SIM card is seriously worn or has poor contact, re-insert the card or replace the card.
5. Back up your data (phone number and SMS, etc.) and restore to factory settings.
6. Once your data is backed up, restart your phone or update it to the latest version.
If the issue persists, contact our Customer Support for further assistance.