a) Ensure volume is set to maximum through Mobile Phone itself

b) Ask CX to use suitable size of ear tips and wingtips

c) Ask CX to use other music APP/music player as different songs/videos app have different audio quality with different Mobile Phones

d) Ensure cleaning of ear tips and validate this by image and ask customer to clean it carefully

eChances are, you might have an issue with the mobile. You can check if the headset is working well using a different mobile. 

If the issue still persists with an alternate device please raise a complaint on our support portal.