You will be invoiced by SendCloud every two weeks. On your invoice you will also find your return shipments and shipments that have had an extra delivery attempt. This also applies to shipments that have received a change of address or another instruction, if the carrier charges extra for this of course.
Because the carrier must process the shipment again when it gets returned, redelivered or changed, you are charged for this. You can find this specified on your invoice.
You can find the invoices in your Settings > Financial overview in SendCloud.