I had a similar issue with O2. I phoned to cancel once and was told not to cancel till the last day of the contract, then I phoned on the last day but the computer system was down so the advisor couldn't do the cancellation but told me that she would note on my record that I had cancelled. Following this they tried to bill me, so I phoned back and kicked up a fuss. Happily I had chat conversations (they send you a transcript) conforming what i had said so I was able to sort it reasonably easily. If you have cancelled the DD with your bank though, they should not be able to reinstate. Maybe, as factor suggests, there had been a call on the DD just before you cancelled it. otherwise go and kick up blue murder at your bank. I bank online. You can cancel your own DD's instantaneously and also see what has been called on them but not yet paid.