debit query

I had a tracking unit with netstar, then my vehicle got written off in July 2015.. called in to cancel the netstar policy as car had been WRITTEN OFF was made to pay cancellation fee of 800 which i paid WITHOUT GIVING THEM ANY STORIES... ... then this month noticed on my bank statement that netstar was still debiting on my account even after cancellation as specifically told them that car has been WRITTEN OFF and kindly asked for them to cancel my policy... have made numerous calls to the call center still no satisfactory response, as have been paying for a service which i cannot utilize, which according to my knowledge was cancelled as paid their cancellation fee which they stipulated