.01 Customer Billing.

A. Billing Information. Bills to customers shall be rendered at least monthly and shall contain a clear listing of all charges and credits. For purposes of clarity the customer's bill shall include the total amount due supported by the following data:

(1) The charges, including applicable federal and local taxes for:

(a) Local monthly services from the current to the next bill date;

(b) Additional message units, if appropriate, for the month before the billing date;

(c) Toll calls and telegrams, if appropriate, placed before the billing date;

(d) Other charges and credits with appropriate explanation.

(2) The amount of the balance due carried forward from the prior bill after application of payments received up to and including the billing date.

B. Payment Date. All regular monthly customer bills shall state the date by which the customer shall pay the bill in order to avoid suspension notice or other utility collection procedures. All toll charges of the customer shall be itemized so as to facilitate their identification. Each utility shall comply with reasonable and feasible customer requests for itemized statements of charges.

C. Wrong Number. A charge may not be made for a dialed wrong number if the utility is notified promptly, except for certain services, as specified in the utility's tariff.

D. Overcharge—Undercharge Adjustment. When a customer has been overcharged or undercharged for services because of incorrect application of the rate schedule, inaccurate measuring of services rendered, incorrect calculation of charges or similar reasons, the amount of overcharge or undercharge adjustment shall be determined separately during the period of time the discrepancy occurred, in accordance with the following:

(1) Overcharge Only. The total overcharge for the period the discrepancy occurred shall be refunded or credited to the customer.

(2) Undercharge Only.

(a) Unless authorized by the Commission, retroactive billing may not be for undercharges which occurred more than 12 months before the discovery of the error. A utility may seek the Commission's authorization for retroactive billing for undercharges which occurred more than 12 months but not more than 3 years before the discovery of the error if the customer knew, or reasonably should have known, that the bills were in error. The utility's request to the Commission shall be in writing and shall explain the factual basis for the request to the customer with a notice of the customer's right to write to the Commission, within 20 days, if the customer is in opposition to the request.

(b) If the total undercharge is more than 35 percent of the customer's average monthly bill during the preceding 3 months, the customer shall be allowed to enter into an installment plan to pay the total retroactive billing, without interest. In such a plan the monthly payments against the undercharge may not exceed 35 percent of the customer's average monthly bill during the preceding 3 months. However, if the installment plan will not recover within a 12-month period the total undercharge, the monthly payment may be equal to the total undercharge divided by 12 or a number greater than 12.

(c) Unless otherwise authorized by the Commission, the utility may deny service for nonpayment only for that portion of the undercharge applicable to the 4 months immediately before the discovery of the error.

(3) Combination of Overcharge-Undercharge. When a customer's account has items of overcharge and undercharge, the difference of the two items is then determined as the net adjustment in accordance with §D(1) and (2), above.