Cancelling of Debit Order

My husband tried on various occasions to cancel his monthly debit order. Our contract was extended without prior notification. We sent letters and email to cancel but we never receive feedback. When we call, they want a letter in order to cancel on their side but when we forward letters we never get feedback. We don't make use of mweb but they keep on debiting our account on a monthly basis. Mweb need to cancel same and call us back and give our money back from the first time we informed them..