Forced into service i do want

I cancelled my application with national debt advisors within 24 hours of applying. They are now bullying me into using their service even though i cancelled within 24hours. What type of business does not have a cooling off period? Is there such a thing as no cooling off period? They are threatening to debit my account whether I agree or not. And they will send me an invoice for the service I repeatedly told them I do not need anymore. Please help to stop these people from debiting my account. I do not need their service I am sorted with my creditors. In good arrangement with my creditors. I do not want them to mess up my arrangements with my creditors. PLEASE HELP ME .