In determining just, reasonable and sufficient rates the Commission shall give due consideration to the telephone utility’s property devoted to the public service; the revenues received for the service; the reasonable operating expenses and other costs necessary to provide the service; the total earnings required for the proper discharge of the telephone utility’s public duty; the capitalization of the telephone utility and the net income required on its net worth; and such other matters, circumstances and conditions as the Commission may find necessary. But the rates so fixed shall not be higher than necessary to give a fair return to the stockholders.