Right so I've just got a 12 month XBL subscription as my account runs out today, I've clicked renew subscription and its just done it for me. It hasnt asked me to enter my code or anything

How is this possible? I don't have a card registered to my account for it to have taken any money for it? Also if I put on my 12 month code now, will it just add the 12 months on or will I have to cancel the Xbox Live after the year and then add the code?

Note: I'm aware I had to select redeem code but it completely slipped my mind

If you have ever entered your credit card information into your Xbox, it might have just charged your bank account. Might wanna check that?