No utility shall terminate service unless the utility has first offered a monthly installment plan that is just and equitable. Each utility must offer a just and equitable monthly plan to all customers whose service has been disconnected for nonpayment. To the extent practicable, the monthly installment plan should be based on the customer's ability to pay, past payment history, the amount of indebtedness, and the availability of other resources. The monthly installment plan should require a customer to pay current bills and a portion of past indebtedness and may include a provision for payment of interest on the arrears. Such agreement may provide for a downpayment of the arrears provided that no such downpayment shall exceed one-half of the amount of the arrears or three months average billing, whichever is less. Such agreement may be renegotiated and amended where the customer can demonstrate that there have been significant changes in his or her financial circumstances which have arisen due to conditions beyond the customer's control.