Debit order continues despite closing account

I am quite disappointed with your cancellations department. Firstly, when we sold the vehicle that had the tracker fitted during early December 2015, there seems to be nobody who could assist me with cancelling the account. I was told to call various people, who could not help either... I then decided to email and various staff gave different answers. Finally, on 23 December I did receive an email with attachment from Cairn Van Rooi that my account has closed and that the debit order has been stopped. Today, 17 January, I receive an SMS from my bank that the debit order still went through..... How does this work???