Unauthorized over-deduction of debit order

I have agreed, telephonically to a discount and settlement of account if I paid 2 x R890 installments on this account totalling R1790 repayment. To date, I have had 2 x R890 debit orders go off my nominated bank account (September, October & November) totalling R2670. I have tried to reach out via your Whatsapp line, but no one gets back to me. I was also promised a copy of the telephonic agreement to avoid issues such as this from happening, but have not received anything.