(a) No utility shall charge a residential customer for service rendered more than six months prior to the mailing of the first bill for service to the residential customer unless the failure of the utility to bill at an earlier time was not due to the neglect of the utility or was due to the culpable conduct of the customer. If the customer remains liable for any such service and the delay in billing was not due to the culpable conduct of the customer, the utility shall explain the reason for the late billing and shall notify the customer in writing that payments may be made under an installment payment plan tailored to the customer's financial circumstances.
(b) A utility may not adjust upward a bill previously rendered to a residential customer after 12 months from the time the service to which the adjustment pertains was provided unless:
(1) failure to bill correctly was caused by the customer's culpable conduct;
(2) failure to bill correctly was not due to the neglect of the utility;
(3) such adjustment is necessary to adjust a budget payment plan or levelized payment plan as described in section 11.10 of this Part; or
(4) there was a dispute between the utility and the customer concerning the charges for service during the 12-month period.
(c) A utility issuing a billing adjustment increase of $100 or more under paragraphs (b)(2), (3) and (4) of this section shall notify the customer in writing that he or she has the right to pay the adjusted bill in regular monthly installments tailored to the customer's financial circumstances over a reasonable period. An adjustment to increase previously rendered bills more than 12 months after the time service was provided, pursuant to paragraphs (b)(2), (3) and (4) of this section, shall be made within four months of the final resolution of the billing dispute.
(d) A utility adjusting any charge for service rendered 12 or more months prior to the date of issuance shall include with the bill a notice giving the reason for the adjustment.
(e) No utility may render a bill for previously unbilled service or adjust upward a bill previously rendered to a residential customer after the expiration of 24 months from the time the service to which the new billing or adjustment pertains was provided unless the culpable conduct of the customer caused or contributed to the failure of the utility to render a timely or accurate billing.