a) Since there is Dual Pairing in this product, so please ensure if he/she didn't connect the device to other device and forgot to remove it from there

b) Volume level need to check, and set the desired volume level from Mobile Phone itself

c) If using online APP then Check internet connection

d) If using online APP, please check it's compatibility with Mobile Phone and allow permissions from APP Manager in Mobile Phone

e) Mobile phone can also have issues in this case. Check if the device is working well with other mobile phone 

f) RESET the device (Neckband)

Steps to reproduce solution 

You can power off and on the device and voice prompt alert and LED response can let him/her know if the device is connected to any other device or not

Adjust the volume from Mobile Phone only

Sometime, APP malfunctions. Ensure good internet connectivity

App setting can show supported Android or iOS versions

Apply the same connectivity process with different mobile phone as well

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