This usually only occurs if you have assigned a credit card to your XBOX Live account. Simply go into your XBOX live profile using the XBOX 360 Dashboard and remove the credit card from you account.
However after doing this and it comes time for renewal, you will either have to re-supply credit card details or enter in a XBOX Live redeem code (which can be perchased from retail outlets).
In terms of keeping the credit card listed but not having it top up automatically, this cannot be done. As soon as a credit card is added to the XBOX Live Account, top-ups will be automatic.