The owner shall obtain monthly reports from the vendor which identify incidences of unusually high or low usage for dwelling units. The owner shall investigate any unusually high or low usage and, if it is found that a problem exists, or if a written complaint has been filed by the occupant, the owner shall provide a written explanation to the occupant within 20 days of receipt of the monthly report from the vendor. The owner shall take appropriate action to correct the unusually high or low usage caused by factors under the control of the owner.