a) Please check if their is any physical damage with the product

b) If completely no sound at one side then arrange replacement as per policy

c) if Alternate is working go for reset or put your phone on Airplane and check 

Reset Process: 

1- Remove device name from Bluetooth Interface

2- Long press the "+" & "-" key together for 3 seconds

3- Red and White LED will start blinking that shows device has been reset

If Still issue persist please go for replacement