Unauthorized debit order

Last month on the 27th of February i missed a payment for vehicle finance , then i contacted Wesbank and i spoke to a certain lady to make arrangement that they must collect the installment on the 16th of March of which they did so as arranged, however on the 18th of March they processed another debit order which i wasn't notified or made aware of, and i didn't make provision for such an amount to go through my account, they caused me unnecessary unpaid bank charges, i need someone higher to call me and explain how did that happen, and some clarity on my account asap... This is so unacceptable and a very huge inconvenience for me, because it made my account reflect bad... I demand answers...