Okla. Stat. tit. 17, § 17-121: Commission has power of court of record regarding refunds

The Corporation Commission is hereby vested with the power of a

court of record to determine: First, the amount of refund due and

any interest owing upon such refund in all cases where any public

service corporation, person, or firm, as defined by the

Constitution, charges an amount for any service rendered by such

public service corporation, person, or firm, in excess of the lawful

rate in force at the time such charge was made, or may thereafter be

declared to be the legal rate which should have been applied to the

service rendered if no legal rate was in force at the time such

charge was made; and, second, to whom the overcharge should be paid.