Hertz said the mechanical key is "lost"
We rent a car from Hertz last weekend. After we returned the car and dropped off the key in the box, we got a phone call from Hertz the next day saying that they got the key fob but the mechanical key is missing. We never used the mechanical key in our trip and didn't even notice if there was a mechanical key when we picked up the car. The staff insisted that the mechanical key won't accidentally fall apart unless we manually pull it out. They have charged us $100 per day after we returned the car. And they never respond to our message or phone call after.
Am I liable for these charges? What would be the best course of action at this point in time? Especially we never use the mechanical key, we really don't understand how come it could get lost
Any help/advice would be very appreciated