After the hearing the Commission by its order shall either confirm, modify, or vacate its former order, in conformity with what is found to be just and reasonable, and an attested copy of the order of the Commission must be immediately served on the utility affected by registered mail or otherwise, as provided by law. In case the original order of the Commission is confirmed or modified by making the order more favorable to the utility affected, the rates prescribed by the original order of the Commission or the modification of the order, as the case may be, are operative as of the time fixed by the original order. The utility affected shall put the same into effect as of the date fixed by the original order.