Dissatisfied!

I am extremely dissatisfied with Vodacom's service, I have a contract with them and for the past 2 month they have been debiting my account on the wrong day (when there is obviously not enough funds in my account).Upon agreement of the contract I have asked Vodacom to please debit my account on the last day of the month if the last day of the month is a weekend they need to debit my account the next business day. I have called Vodacom last month to resolve the issue and they agreed that the debit will take place according to my pay date and that the late fees will be removed as it was their fault for not debiting the account on time,This month the same issue Vodacom has tried to debit my account way before the end of the month resulting in an unpaid debit,there has been enough funds in my account for vodacom to debit as of the last day of the month which is my pay date,Vodacom has not tried to debit my account again and now I am receiving notifications that my account is in arrears.I am not happy with the way Vodacom continues to process incorrectly.