If you want to avoid the complicated system set up by AFIP, then don't order anything from abroad, especially if you don't have a DNI, a CUIT, a clave fiscal, a local bank account, and know your local AFIP agency office and the language. It's a lost cause. Find what you need locally or do without it.
I decided to visit my local AFIP office and see what response I'd get in person when I showed them a printed DECLARACION SIMPLIFICADA DE ENVIOS POSTALES INTERNACIONALES and VOLANTE ELECTRONICO DE PAGO. After waiting about 15 minutes, I discovered that I was on the wrong floor of the building. I got the attention of a man behind the counter who then asked another to look at the documents. He told me to inquire at the post office, which I did already, or to make payment at PagoFacil, which I tried to no avail. He then went to another department to ask a manager. That man referred him to a woman at the front desk to help me. She basically told me what I know -- that I could only pay for the door-to-door service by the post office through a bank account. I'm going to ask a friend to make payment through her bank account at a Banelco. I will report on how long it takes to receive delivery of a package that was shipped early September.