INCORRECT DEBIT ORDER DATE

I took out a credit shortfall policy on my car finance and agreed that my pro-rata debit order for August would be processed on the 25th August, as that's when I get paid. Yet last night the debit order went through on my account and because there were insufficient funds available the amount was reversed and I was charged R25.00 penalty fee. PLEASE THIS NEEDS TO BE SORTED OUT. This is not what we agreed on. Had I known this was going to take place I would have ensured there was money in the account. I await your urgent response.