Bad Service

I have 2 accounts which are currently on a minus and have since made an arrangement to pay the accounts R500 each a month and would settle the accounts in full at the end of May when I recieve a lump sum. Surprisingly this morning ABSA has taken R8300 off my other account and settled one of the accounts. I didn't agree to a debit order nor an interaccount transfer. Why would ABSA take my money without my knowledge. This is so unlike a bank that looks after their needs of their customers. I never consented to any interaccount transfer. Someone please assist