Chances 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 presist with an alternate device proceed with unpairing and pairing once again:
How to unpair:
1. Tap and hold the Bluetooth icon on your mobile
2. Tap on "Noise Airbuds"
3. Click on Remove / Forget Noise Airbuds
Pairing with a new device:
1. Remove the buds from the case
2. Turn on the bluetooth of your device
3. Search and Select the name “Noise Airbuds" from the list of available Bluetooth devices.
4. Please select PAIR. The pairing procedure will be completed.