As odd as it may sound, in Argentina you have to provide an ID to buy a SUBE card, so I gave what I had at the time: my foreign passport. You also have to know that one individual can have just one SUBE at time, so your DNI can be associated with one card and no more than one.
Hence, my card was associated to a Foreign ID (Documento Extranjero) number. Now, since in Argentina IDs use digits only, whereas passports have one or two letters and some numbers, my foreign passport (A123456) was recorded in the system as just 12345 as the textfield didn't allow for the letter A.
I used to check my balance online in the past, but after a few years they made a mixup in their database, and my 12345 number was now filed as and Argentinian ID (instead of Foreign ID), so it was associated with another person, a lady named Luciana Maria.
At first, I thought I was sold a stolen SUBE, but when I saw the lady's DNI number I recognized my passport number. I went to a Centro SUBE and explained the glitch, and there was nothing to be done: I needed to get a new card, or Ms. Luciana Maria could have cancelled mine at any time. No balance transfer was possible, so I was sure to use all of my balance before cancelling Luciana's card.
When they give you a new card, you are charged $50 at the first top-up of the card.