b) Billing Time Period for Refunds and Credits Due to Overcharges Resulting from Utility Error:

1. 1) A utility shall issue a refund or credit to a customer's account for the full period of time during which an overcharge occurred, so long as either the utility or the customer has retained billing records that would allow determining a refund or credit.
2. 2) A utility shall retain billing records and ledgers that would allow determining a refund or credit for a minimum of two years from the current date.
3. 3) A utility shall not be obliged to issue to a customer a refund or credit that extends into a time period during which that customer was not the customer of record. Exceptions may be made when the utility issues a refund or credit as a result of a Commission order.

c) Overpayment without Utility Error:

1. 1) If the overpayment is the result of the customer paying more than the amount due on the bill, then the overpayment shall be noted on the customer's next bill statement, itemized to indicate the credit balance.
2. 2) If the customer requests that the money overpaid be refunded to him/her, then the utility shall be obliged to do so as long as the overpayment credit amount exceeds 25% of the customer's average monthly bill. The refund shall be made within 10 business days after the utility confirms that it has received the money involved with the overpayment.
3. 3) This subsection (c) shall not apply to any overpayment that results from payment on the customer's account by a State or federal assistance agency. Any such overpayment or credit on the customer's account shall be handled in the manner specified by the State or federal agency.

f) Credit to Bill Statement or Direct Refund to Customer:

1. 1) Regular billing: For active service or transfer of service accounts, the utility shall either issue a credit to the account or, if the customer requests it at any time, make a direct refund to the customer so long as the credit balance exceeds 25% of the customer's average monthly bill.
2. 2) Final bills: When the credit amount exceeds the total amount due on a customer's final bill, the utility shall issue a direct refund to the customer.
3. 3) Exemptions from refunds: A utility shall not be obliged to issue a refund to a customer for a credit balance accrued as the result of Commission approved billing programs or rates that specifically disallow the issuance of refunds, or when the customer owes the utility a past due amount for the same class and type of service at another location.

g) Time Limit to File Complaint:

1. 1) Excessive or unjust charges: All complaints for the recovery of damages shall be filed with the Commission within 2 years from the time the produce, commodity or service as to which complaint is made was furnished or performed. [220 ILCS 5/9-252]
2. 2) Refunds for overcharges: When a customer pays a bill as submitted by a public utility and the billing is later found to be incorrect due to an error either in charging more than the published rate or in measuring the quantity or volume of service provided, the utility shall refund the overcharge with interest from the date of overpayment at the legal rate or at a rate prescribed by the Commission (see Section 280.40(g)). Refunds and interest for such overcharges may be paid by the utility without the need for a hearing and order of the Commission. Any complaint relating to an incorrect billing must be filed with the Commission no more than 2 years after the date the customer first has knowledge of the incorrect billing. [220 ILCS 5/9-252.1]