Can I cancel a shipment?

Yes, yourself in My DZH, as long as no parcel of that shipment has arrived with us yet; you give a reason and the shipment is closed without any charge. If a parcel has already arrived, you can no longer simply close the shipment, because the box is with us and has to go somewhere: you then choose between shipping it to your address after all, returning it to the shop with the shop's return label, or disposing of it. A label that has already been created can usually still be withdrawn as long as the carrier has not collected the parcel; after that no longer. If you accidentally created a wrong shipment without parcels, just delete it; empty shipments cost nothing and expire by themselves after a while.