MFC Nedbak installment date

I have my car financed with MFC and they are supposed to run a debit order on the 1st of every month. They didn't debit on time the two months ago, i ended up making an arrangement to now pay that installment broken down into monthly arrangements because the full installment was no longer available. Arrangements have interest because they are essentially Arrears. Im literally left with one more month for the agreed arrangement but my initial installment is still supposed to go through. Today is the 1st of the Month, there has been money in my account since yesterday already and still no debit order from them has went through, which means when they try and debit, there wont be funds anymore, which means account will now be in arrears and which then means another arrangement. Why are you debiting when you want and not on the agreed date?