Then be prepared to have a Court Order issued by 3 and for a debt collecting agency to be employed to recover the money you owe them. Cancelling a Direct Debit without going through the full disputes procedure is just about the worst thing you could do. In the eyes of the law you are in the wrong and you could find yourself with a mark on your credit record that will cause you untold grief in the future.
Based on what you said in your previous posts I don't think you have a case to argue but simply stopping a payment won't get you anywhere.
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.