Process When a Utility Issues an Adjustment of Bill as Prescribed in COMAR 20.55.04.05 to a Supplier Providing Supplier-Consolidated Billing. The supplier shall refund or credit the customer if the bill adjustment results in an overcharge. The supplier may attempt to collect the amount due from a customer if the bill adjustment made by the utility results in an undercharge. Process When a Supplier Determines that It Has Incorrectly Billed a Customer. If a supplier determines that the bill adjustment results in an overcharge, the supplier shall refund or credit the customer. If a supplier determines that the bill adjustment results in an undercharge, the supplier may attempt to collect the amount due. Restrictions Regarding Supplier Billing Undercharges Under §B(2) of this Regulation. A supplier may not issue a bill adjustment for an undercharge if the price used to calculate the bill adjustment was not previously disclosed to the customers by contract or as required in COMAR 20.59.07.13. The supplier may retroactively bill an undercharge that is less than 12 months old without Commission authorization. A supplier may seek the Commission’s authorization for retroactive billing for undercharges which occurred more than 12 months but less than 3 years before the discovery of the error if the customer knew, or reasonably should have known, that the bills were in error. If an undercharge is greater than 12 months, the supplier shall provide a written notice to the customer that explains the factual basis for the undercharge together 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. Supplier Billing an Undercharge Under §A or B of this Regulation. If the total undercharge is more than 35 percent of the customer’s average monthly bill during the most recent 3 months of service with the supplier, the customer shall be allowed to enter into an installment plan to pay the total retroactive billing, without interest. In the installment plan under §C(1) of this regulation, the monthly payments against the undercharge may not exceed 35 percent of the customer’s average monthly bill during the most recent 3 months of the customer’s service with the supplier. However, if the installment plan will not recover the total undercharge within a 12-month period, the monthly payment may be equal to the total undercharge divided by a number no less than 12. If requested by a customer, a supplier shall provide a means by which any undercharge may be paid in installments over a reasonable period of time, but not less than the same period over which any undercharges were incurred. If a supplier is required to provide an installment plan due to a utility-identified bill adjustment in §A of this regulation, the unbilled regulated utility charges of an installment plan as required by §C of this regulation may not count toward the limit on the number of days a supplier has to sell customer arrearages to the utility under COMAR 20.59.05.10 D(2).