Payless Car Rental review: Car rental return service

I rented a car from payless seatac from fri aug 28 to mon aug 31. I picked up the car near the avis station as directed and returned to the same place. A lady came by and placed a hand held device to the drivers windshield are and I hear a beep_ she said I was good to go. Now I just recieved an e mail telling me the car was 3 days over due and to return it. The customer service agent taking my issue did not seem to care.