Unauthorized debit on my cheque account

I am so disappointed in my bank, Absa. I have been a client for more than 15 years and last night they just debited my cheque account with R8160,19 without my consent for a 1-month personal loan instalment due which I have made arrangements for. The arrangement of paying R2073 extra each month until such time the error instalment is settled was too late for the September 2023 debit order as I was told it must be loaded at least 7 days prior to the debit order date. It was agreed that the new instalment would be debited from October 2023. I am not disputing the money owed however why not debit the R2073 arrangement amount and not the entire outstanding amount? Who authorised the debit and what if I had no money in the cheque account? I went to the bank this morning and they couldn't refund the payment and referred me to the collections department who refused to refund me and said I must take it up with complaints as the arrangement was for September 2023 and mind you, my normal instalment went through on 15 September. What horrible customer service. That money is due to be paid for rent tomorrow. I think this is why people switch to other banks. Unhappy client.