It works like Facebook. You're currently subscribed via your Credit Card.
Therefore, you can't remove the card now, and if you use a pre-paid code you get slapped back onto auto-renew. I don't know the correct term for it, but it just seems like a standard check.
If you "delete" your account on Facebook, you have to wait X days before it's fully removed. If you log back in, the deletion is stopped.
I've used pre-paid codes since over 2 years now, and I have never been put onto auto-renew. Because I waited until my subscription ran out, and I removed my card.
So stop spreading FUD, lawyer.