Debiting my account after account has been closed

My husband has been trying for 9 months now to terminate his cell c contract because of the terrible drop in service all round .we called cell c callcentre and they confirmed the cancellation date 5th October 2017. We called in June ,july and august and cell c confirmed last debit order will run end of September .We received an sms confirmation of the cancellation .to our surprise cell c debits the account again end of October for apparent usage in September .if we allowed 30 days notice and all was confirmed including last debit order date and they just debit the account. Where is the tcf and how can you debit an account on a closed account.Their call centre agents keep going on about how we are not understanding yet they not understanding a cancellation was done .dates were confirmed payments were finalised i now want my money back .I will not wait for my money as this is theft just because cell c has my bank.details they feel free to just do as they please.The worst service provider.