No transportation company shall charge or demand, or collect or receive, a greater or less or different compensation for the transportation of passengers or property, or for any service in connection therewith, than the rates, fares or charges specified in the tariffs or schedules of rates in effect at the time, except as provided by law or the Public Service Commission, and the rates, fares and charges duly filed and posted in accordance with the provisions of this chapter shall be the legally applicable rates, fares and charges, but the commission may prescribe such changes in the form in which such tariffs or schedules of rates shall be issued by transportation companies as may be found expedient.