No warning about penalty fee

At the beginning of September my debit order for my Vodacom account was returned because I did not manage it correctly, so when I realized this I immediately phoned the customer care and explained the situation to them and asked to pay the outstanding amount. I asked that they specify what the amount was. The lady told me R122.49, I then asked about the penalty fee, and she said there is supposed to be one but it is not there, I can just pay the amount. I then left it at that. I also received an sms confirming that my account was up to date and paid. Come the end of September I get the surprise of an extra R100 being deducted from my bank account, so I phoned them again, and to no surprise they say it is the penalty fee for the previous month's returned debit order. Now I would have had no problem to pay it the previous month because it was my mistake, but the fact that when I called to settle it they said there is not a penalty fee and then later deduct it angers me. I received no notification that they were going to deduct this, and as I leave exactly the right amount of money in my account for all my debit orders, this resulted in my other debit orders being returned and me having to fix a great mess again this month because of Vodacom's penalty fee. I have already called Vodacom about this and would like them to compensate me by cancelling the penalty. I spoke to a consultant there, he was not very helpful and said he will log a query. It has now been more than a week and I have not received feedback from them. This to me is poor customer service.