When the commission finds that the rates, fares, tolls, rentals, charges or classifications, or any of them, demanded or collected by any public service corporation for any service, product or commodity, or in connection therewith, or that the rules, regulations, practices or contracts, are unjust, discriminatory or preferential, illegal or insufficient, the commission shall determine and prescribe them by order, as provided in this title.
A.R.S. § 40-203