Billed on cancelled policy for 9 months

I have a cancellation letter for a Gap cover policy I took out in May of 2015. And after changing my mind and cancelling within the cool off period of 30 days I received this letter, however they keep debiting my account and no emails or forwards of my letter seem to get any response. I have cancelled the debit order with my bank a few times but today again it was taken. I woul like this resolved asap