Without knowing the Gamertag or any info at all about the account it would be hard to cancel it through Xbox.
If there's even something which could help get information about it, you would be best off contacting Support as linked above.
If you do not have any account information at all you will unlikely to ever be able to regain access to it.
If you were to block the payments through the bank, it will get the account banned (I believe these can be overturned, but it leaves a serious Enforcement action on the account) because to Xbox it will appear as if you are trying to have a Live subscription
active but blocking them from taking payment for this. Note that proceeding with this action is not advised at all in any official capacity and risks hurting your account's standing on Xbox Live.
I reiterate that any info you have about the account will help you regain access. The email could be the same as a Hotmail/Outlook account, one you use on a Windows Phone, or for SkyDrive... any Microsoft product or service, really.
Xbox Forums moderator. Xbox MVP. r/xboxinsiders moderator. Twitter: @13mxn
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