See our money order guide. Step 1: Contact the issuerwho will ask you to start the cancellation process by completing a request form. If it was a postal service money order, visit a post office to fill out the form. You might also be asked for the name of the person givd company you were paying and a brief description of how the money order was lost. Step 4: Submit the cancellation request form and pay a fee. Some issuers, including Western Union, let you email, fax or mail the request.