My wireless headphones have stopped working. When I plug them in to charge, the light comes on red/pink to indicate a charge is needed, and turns blue when it has a full charge. But when I unplug it, the blue light goes out, and turning the on-off switch does nothing. Also, I’ve tried pairing this while connected to power and with the blue light on and it does not appear on my iPad. Is there any way to troubleshoot this? Could the battery inside the wireless headphones be dead/defective? Something else?