Lenovo — Lenovo vibe k5 notification sound very low

Address:

Ahmedabad, Gujarat

Sir,
I'm using lenovo vibe k5 . From past 1month i'm facing ringtone sound issue.
Even with the highest volume of ringtone and notification tone, the sound comes very low. i missed important notification many times .Whenever i got a any massages, i'm unable to get notification of massages due to low voice of notification even at highest ringtone level in settings. i set notification tone with maximum volume. but same issue.

Please help me to resolve this issue.

Thank you.