What happens with your Xbox Live when the debit card expires, does it stack up payments?

I have xbox live and the debit card i was using to pay for it has expired and my live has continued, i recieve e-mails letting me know that the card has expired each month warning me that my live will be cancelled however it hasnt, its been like this for about 6 months now. I was wondering do the payments stack up or is it a technical glitch? And yes I do have another payment method saved, would it use that instead?|||No it just lets you know via email that your debit expired, and then it cancels you live membership. Then it asks for new debit card. It used to stack payments, and if you didn't pay, they banned your account