First please try turning your device off and on.
If the problem still persists, please go to the Message tab and click on the Settings icon.
Then click on Help center and submit a request with the answers to these questions and press send.
1. If this problem occurred with one specific user or with all users.
2. If this happened while meeting new people or while using the video call feature.
3. If the volume of the device is on mute.
4. If there are no sounds coming from other apps as well.
5. Are you using earphones/headset or Bluetooth earphones/headset?