Cancellation of debit order

As per my previous request, this is an ongoing matter and it appears that nothing is being done about it. In June 2015 I requested cancellation of services which appears this company cannot do. Each time they say go and dispute it at the bank which takes 7 days to get the money back and I still have to pay the debit order fees. I am unable to put in a stop payment on this because each month the amount differs. Why is it such a problem to cancel a debit order. I'm really tired of this service