Whenever there is filed with the Commission any new charge, classification, or practice, the Commissioner may either upon complaint or upon its own initiative without complaint, upon reasonable notice, enter upon a hearing concerning the lawlessness thereof; and pending such hearing and the decision thereon, the Commission, upon delivering to the utility affected thereby a statement in writing of its reasons for such suspension, may suspend the operation of such charge, classification, regulation, or practice, but not for a longer period than eight months beyond the time when it would otherwise go into effect; and after full hearing, the Commission may make such order with reference thereto as would be proper in a proceeding initiated after it had become effective. If the proceeding has not been concluded and an order made within the period of the suspension, the proposed change of charge, classification, regulation, or practice shall go into effect at the end of such period, but in case of a proposed increased charge, the Commission may, by order, require the interested utility to keep accurate account of all amounts received by reason of such increase, specifying, to the extent feasible, by whom and in whose behalf such amounts are paid and upon completion of the hearing and decision may, by further order, require the interested utility to refund, with interest to the persons in whose behalf such amounts were paid, such portion of such increased charges as by its decision shall be found not justified. At any hearing involving a charge increased, or sought to be increased, the burden of proof to show that the increased charge, or proposed increased charge, is just and reasonable, shall be upon the utility, and the Commission shall give to the hearing and decision of such questions preference over all other questions pending before it and decide the same as speedily as possible.