Extra charge query

My Discovery account was handed over to them in November 2024, owing R1517,00. I contacted Shapiro Shaik Defries & Associates to set up a payment plan and I was told that my account was sitting at over R2200 and I asked for a detailed statement so that I could see the accumulation of interest. I was surprised to see charges for emails or letter that had been sent to me, totalling 13. I was charged somewhere in the region of R24 each time. Meanwhile I have only ever received 3 emails from them and I have proof of these. I have asked them to provide me with proof of the emails they have sent to me but I have not received a response. How do I dispute this?