CANCELLATION OF CONTRACT - DEBIT ORDER STILL BEING DEDUCTED

DATA CONTRACT CANCELLED ON 6 AUGUST, AFTER CONTRACT EXPIRED. AFTER CANCELLATION MONTH PERIOD ON 6 SEPTEMBER ALL THE DATA THAT WAS LEFT WAS TAKEN OFF. NO DATA FROM 6 SEPTEMBER, BUT STILL HAD TO PAY THE FULL AMOUNT ON 30 SEPTEMBER. NOW ON THE 30TH OF OCTOBER THE DEBIT ORDER FOR THE FULL MONTH WENT OFF FROM MY ACCOUNT. HOW CAN THEY STILL BILL ME IF I DON'T EVEN GET THE DATA. TRIED PHONING CELL C, THE REPRESENTATIVE TOLD MY HUSBAND IT WAS FOR NOTICE PERIOD, BUT WAS GIVEN FROM 6 AUGUST TO 6 SEPTEMBER.