Section 118 - Payment to an authorized payment agency1. In any case where a public utility company or municipality rendering equivalent utility services permits its customers to pay their bills to a payment agency authorized by the corporation or the municipality for collection of bills, the date of payment to such authorized payment agency shall be the effective date of payment of such bill, and the payment shall be regarded as if it were paid directly to the corporation or municipality on such date. Where a customer of such corporation or municipality has paid a bill to an authorized payment agency on or before a designated due date, no penalty or extra charge shall accrue on such bill for the reason that the payment did not reach the corporation or municipality on or before the designated due date. Notwithstanding the provision of this section, payments to authorized payment agencies by residential customers shall be governed by article two of this chapter.2. Backbilling. Except as provided for residential utility service pursuant to article two of this chapter, no public utility company or municipality may render a bill for previously unbilled service, or adjust upward a bill previously rendered, to a residential customer after the expiration of twenty-four months from the time service to which the bill or adjustment pertains was provided. This provision shall not apply when the culpable conduct of a customer caused or contributed to the failure of the company or municipality to have rendered timely or accurate billing.3. Credit or refund of overpayments. (a) The commission shall have the power to require a public utility company or municipality to provide a refund or credit to a customer when a payment has been made in excess of the correct charge for actural service rendered to the customer.(b) If a residential customer becomes eligible for a lower rate because he or she changes the character of the service received and if excess payment resulted from the failure of the customer to notify the utility or municipality providing service of a change in the character of service received or from the failure of the utility or municipality to change the rate after such notification by the customer, such a customer will be entitled to such lower rate from the date the change occurs but such a customer shall not be entitled to such lower rate for more than twenty-four months prior to the giving of actual notice to the utility or municipality providing service.N.Y. Pub. Serv. Law § 118