It looks like you really don't have an idea how warranty of an HDD works? Their warranty is based on serial number and by providing the serial number (in case of WD) or serial Number and Model Number (in case of Seagate), you can see how much warranty is left for the product and for claiming it, you don't need any invoice. In case of WD, OP can directly logged an complain through the Web site and WD will arrange an courier pickup from his home.