Billed after contract cancelled

Good Day,I was offered the premature cancellation on 2015/09/08 which i was requested to pay to cancel contract, i paid the amount at Vodacom outlet in Menlyn Pretoria.I was then advised that contract will be cancelled in 24hours as all amount due was paid on contrcat. To my suprise ,the debit order amount went through on 01/10/2015 and i requested that to be reversed as i paid all amount due on my contrcat and i have never used the data after apyment was made as all services was discountinued