What do I do if calls disconnect automatically?

Please follow the below steps:
1. Turn Airplane Mode on and off, and then dial again.
2. Go to settings>Network&internet>SIMs>Enable 4G Calling or disable 4G Calling to try again.
3. Calls are largely affected by the network. Try changing the network environment and call again.
4. Try a different SIM card to check if it is better.
5. Update the firmware of the phone to the latest version
6. Back up phone data and restore factory settings.
If the issue persists, contact the Nothing Support Team for further assistance.