I had the same problem.
I cancelled on 27 September, but received a bill for November. I used the online chat support service and they confirmed that the bill was a mistake and that it would be rectified in December.
My December bill now states that they owe me money, but also states "Payment details for the balance of R 615.00 were not available on 08 Dec 2017. Please pay immediately. If you have paid the arrears, please ignore this message." I of course did not pay for November, since I cancelled in September. Yesterday the consultant on the online chat again confirmed that my account is closed and settled. I must phone 10210 to get my R200 paid out.
I have of course kept copies of these conversations...