1. Please turn up the phone.
During the call, press the volume increase button to increase the call volume.
2. Confirm whether the Bluetooth device is connected.
If the mobile phone is connected with a Bluetooth device, it can play sounds through Bluetooth devices, such as Bluetooth headsets and car Bluetooth. You can go to Settings-Other Networks and Connections and turn off the Bluetooth function to view.
3. Check whether the cell phone signal is good.
If the cell phone signal is not good, it will affect the call quality. It is recommended to go to the area with good signal for call test.
4. Comparative test
Comparing different contacts, if a number is abnormal, it may be because of the other person's mobile phone or network.
5. It is recommended to open VoLTE HD calling service (contact the operator to open it).
If the local 2/3G call network environment is not good, it is recommended to contact the operator to open VoLTE HD call service and try again. When the VoLTE function is turned on, the HD icon will be displayed in the signal bar.
6. The new version of the system improves the compatibility and stability, and optimizes the performance. Please go to Settings-System Upgrade to check the system version information. If it is not the latest version, it is recommended to upgrade the experience.
7. If the above methods can't be solved, please back up the mobile phone data in advance and take the mobile phone and purchase voucher to the vivo customer service center for testing.
Tips: It is suggested to call the staff of the service center in advance when going to ensure that the staff will go again during normal working hours, avoid running empty and pay attention to safety on the way back and forth.