(1) A public utility may not charge a customer a rate or an amount for a service that is different from the rate or amount prescribed in the schedules or tariffs for the public utility.
(2) A public utility may not charge a customer a rate or an amount for a service that is different from the rate or amount the public utility charges any other customer for a like and contemporaneous service under substantially similar circumstances.
(3) A difference in rates or amounts charged does not constitute a violation of subsection (2) of this section if the difference is based on:
(a) Service classification under ORS 757.230;
(b) Contracts for services under ORS 757.516; or
(c) An optional schedule or tariff for the provision of energy service that takes into account a customer’s past energy usage and provides price incentives designed to encourage changes in the customer’s energy usage that correspond to changes in the cost of providing energy.