Hp Attorneys

Good day I had an account handed over by Vodacom to HP attorney. Last month I paid the account and I was given a settlement letter. Today I receive a letter saying that I owe them R194. 54 for there legal fees. I am so angry as I made sure I paid the amount I owed them. For them to try and get so much money from me is wrong. I have proof of messages of the amount I needed to pay. Can they stop harassing me with messages as I have settled the account and I have proof.