I can't make a call on my mobile phone. The phone said that the call failed and it was unavailable.

1. Confirm whether the signal of the mobile phone card is normal: weak or no signal of the mobile phone card will make it impossible to make calls and make calls.

2. Switch flight mode: You can try to switch flight mode, re-register the network and try again.

3. Confirm whether the mobile phone card has call barring service: Some mobile phone cards of operators have call barring service. If your mobile phone card has restricted outgoing calls, some or all calls will be restricted. Please consult the operator's customer service for details.

* Note: Go to Settings-Applications and Permissions-System Application Settings-Telephone-call barring to see if call barring is turned on.

4. Confirm the status of the mobile phone card: ensure that the phone bill balance of the mobile phone card is sufficient. If the phone is down due to arrears, please restart the phone after recharging successfully.

5. It is recommended to open the VoLTE HD calling service (contact the operator to open it): If the 2/3G calling network environment in your location is not good, it is recommended that you contact the operator to open the VoLTE HD calling service and try again. When the VoLTE function is turned on, the HD icon will be displayed in the signal bar.

6. Comparative test: I suggest you compare the mobile phones with the same carrier card around you. If there is this phenomenon, it may be caused by the poor network quality in your location. You can move to another place and try again.

7. Upgrade the system or reset the network settings: Please upgrade your mobile phone to the latest version. If the mobile phone is the latest version, I suggest you go to Settings-System Management-Backup and Reset-Reset Network Settings-Select the corresponding SIM card-Reset Settings, and then use it to check.

* Note: Resetting network settings will reset WLAN, mobile data network and Bluetooth connection records;

8. Service center testing: If the above methods fail to solve your problem, please back up your mobile phone information in advance and bring your mobile phone and purchase certificate to vivo customer service center for testing; Go to the official website-My-website of vivo and select your current city to get the address and contact information of the customer service center.