Unfair repayments arrangements

I have a personal loan with Capitec and recently requested them to increased my premiums in the attempt of paying it off quickly. I contacted Capitec via whatsapp and got through to Noxolo who gave me a new payment amount that I felt was less than what I was prepared to pay. I requested her to check for me again and I Gave her a higher amount that I am willing to pay and then she advised me that the maximum amount I can pay was the previous amount she gave me. I found that to be a bit ********* as I obviously have a few hundreds to spare and want to put it towards my payment. I am logging this in the quest to get someone to make this make sense to me. Is this in line with national credit act as I feel I am not being treated fairly.