Cancelled contract still being charged for

Back in June I canceled my contract with DSTV and they confirmed in an email that it had been canceled. I have subsiquent to that cancellation received invoices and emails about outstanding amounts for the month of October. In other words canceled in June therefore with one months notice I paid up to end of period July/August and still received billing for October and now they have a debt-collector phoning me daily to get the October payment. BTW I have only used my TV since June to view Netflix occasionally and some you-tube. When I complain either by phone or by email I am assured that matter will be resolved but low and behold I still get phone calls from their debt-collector on a daily basis. About 08:00 tomorrow morning there will probably be another.