In the event that any rate shall be filed by any common pipeline carrier and complaint against the same or a petition to reduce the same shall be filed by any shipper, and such complaint shall be sustained, in whole or in part, all shippers who shall have paid the rates so filed by the pipeline carrier shall have the right to reparation or reimbursement of all excess in transportation charges paid over and above the proper rate as finally determined on all shipments made after the date of the filing of such complaint.