This could be caused by lint/debris buildup within the headphone jack.
First, please check inside the headphone jack in your phone to make sure there are not dust particles or lint inside. Even the smallest piece of lint can affect the connection. If there are any particles in the jack, make sure to clear them out and try the earphones again.
Next, please carefully take the tips off the earphones and inspect the actual earphones. Make sure there is nothing obstructing the metal mesh covering the driver as this would prevent the passage of sound.
If this does not help, please contact our support team with a copy of the proof of purchase and a photo of your earphones and we'd be happy to assist you to the best of our abilities.