2. Change phone ringtone of the SIM card to check whether it works. “Settings” >> “Sound & Vibration” >> “Phone ringtone”,.
3. Change phone ringtone of a contact person in “Contacts”. You may select a contact person in Contacts. Then, tap upper-right menu icon to set the ringtone.
4. Update the firmware to the latest version: You may check the firmware version in “Settings”>>”System”>> ”System updateS” >>”Check now”.
5. Access to Safe Mode by long pressing power key >>press and hold Power Off >> press OK.
If your phone works well in Safe Mode, there may be some 3rd applications cause this issue. Please reboot your phone and check again if it works well.
6. Backup your data and perform factory data reset.