Whenever the Commission shall find, after hearing, that the rates, fares, tolls, rentals, charges or classifications or any of them, however or whensoever they shall have theretofore been fixed or established, demanded, observed, charged or collected by any public utility for any service, product or commodity, or that the rules, regulations or practices, or any of them, affecting such rates, fares, tolls, rentals, charges or classifications, or any of them, are unjust, unreasonable, noncompensatory, inadequate, discriminatory or preferential or in any wise in violation of any provision of law, the Commission shall, subject to review by the courts, as herein provided, determine the just and reasonable fares, tolls, rentals, charges or classifications, rules, regulations or practices to be thereafter observed and enforced and shall fix them by order as herein provided.