No telephone corporation shall charge a residential customer for previously unbilled service or adjust upward a bill previously rendered when the period for the unbilled service or billing adjustment is more than 24 months prior to the mailing of the bill or the upward billing adjustment for service to the residential customer unless the culpable conduct of the customer caused or contributed to the failure of the corporation to render timely or accurate billing. If the customer is liable for any service and the delay in billing was not due to the culpable conduct of the customer, the telephone corporation shall explain the reason for the late billing and shall advise the customer that suspension/termination of service is not permitted for nonpayment of charges billed in excess of six months after the service was provided and that payments may be made under an installment payment plan. Any such installment plan must be consistent with a customer's ability to pay and for a reasonable period of time that shall not be less than one month for each month represented by the late-billed charges, unless otherwise agreed to by the customer. If requested by the customer, the explanation for the late billing and the installment payment plan will be provided in writing. An adjustment to increase previously rendered bills more than six months after the time service was provided shall be made within four months of the final resolution of the billing dispute.