Cell C *****ing money from me

I missed my debit order with Cell C last month. I called in and made an arrangement that I should be debited on the 26th. But every few days Cell C goes into my account to debit me for money i told them would not be there. This causes me unpaid fees for these returned debit orders. So on top of the money that I owe them i have to pay for a debt that they created. I call in i keep being volleyed between Collections and Customer Care. Nobody wants to take responsibility. Some of them are even dropping my call. This is the worst service ever