Cell C debiting on wrong date

I have a contract with Cell C. On numerous occasions they intentionally debit you before or after your agreed debit order date. On the 31st they debited my account which I normally deposit money into so that debit orders can get their money, but our agreed date is the 1st of every month. Now they blocked my account because of non payment. The money is in the account when I checked on their app they said they are going to double debit on the 01st of March. Now they want me to pay the money into their bank account which last time it happened I deposited money into cell c account then month end they double debited me and I struggled to get a refund. So I would like to ask cell c to stop their inconvenience, when we agree on the contract on a debit date they must comply to it. I won't pay interest that is cell c's fault not mine. Please sort this issue out.