In the wars of commerce nothing covers your ass better than paper, have receipts, canceled checks, and tracking numbers. If you have lost the receipt, check with the retailer that sold you the money order, they should have a record for the time, date, and amount. Check with the company that issued the money order to see if it was cashed, if it wasn't you may be able to cancel it and get a refund. This will take time however, you may have to pay for the item again to keep your source happy in the mean time. Sadly Paypal is a necessary evil in these dark times.