Expired contract but still being billed

Good day We have been being billed for contract that has terminated in August, my sister has made it clear when she was called for renewal that the contract must not be renewed, sent an email and even called again in September when billing was sent to enquire why. The consultant promised that she has sent the cancelation and that there would be no billing for month of October and guess what the billing came through. We haven't used the data because we do not want it and what upset me is that the bill is on my account and my other debits returns unpaid because I knew August was the last month to br debited. The call center is not helping either and the 081180 has no consultant option the voice operator tells the whattsap link is sent to your number download