I ran into the same issue about a year ago and my suggestion would be to phone 1-800-4MY-XBOX
Have your console serial number ready, as well as your gamertag and associated e-mail addresses. Like another poster stated, you're only able to remove it when your Xbox Live Gold subscription runs out, however the staff was able to remove my Gold followed
by removing my card and reimbursing the years I had remaining through codes sent in the e-mail.
Hope this helps.
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