Section 118. Payment to an authorized payment agency

1. 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.