Debit order cancellation

On the 18 of February 2015 I went to Vodaworld to cancel a debit order. I was given a debit order cancellation form. I filled it in and I attached a motivation letter and my ID copy. I faxed all the documents to Vodacom on the same day. But today when I went to Vodacom to make a payment I was told to pay a R100 for the unpaid debit order. Why must I pay that amount because I did cancel the debit order. The capitec bank account is no longer active that's why I cancelled the debit order.