1. Suggest the customer : if the Earbuds and charger case are completely no power, continuously charge it for more than 2H and observe again
2. Replace the cable and charger and check if it works fine
3. Check if there is any dirt inside Bud's copper pillars and charging case pogo pin
4. Charge the Earbuds in comfortable temperature(About 25°C) enviroment and try again
5. If the above trying doesn't work, replace or refurn for customers