100. When a subscriber's telephone is reported or found to be out of order, it shall be restored to service as promptly as possible but, in the event it remains out of order in excess of forty-eight (48) consecutive hours after knowledge by the company of the interruption, the utility shall, upon request, refund to the subscriber the pro rata part of that month's charges for the period of days during which the telephone was out of order. This refund may be accomplished by a credit on a subsequent bill for telephone service.