FNB ********!!!

So I had a credit card that was handed over to your ******** which are MBD Attorneys. I asked for a settlement letter and had agreed to pay by the 31st of January 2020. Mind you I've been asking for this letter since DECEMBER 2019. I only got it on the 3rd of February 2020. It gives me 7 days to pay the amount on the letter. I made the payment on the 8th of February 2020. Now I get a call telling me that there's an interest amount of R170 that I need to settle. HOW when there settlement letter clearly gave a different amount? I'm so frustrated because I just want this over and done with!!! The harassment I've been getting from MBD is absolutely disgusting! I refuse to pay that extra R170 because the initial amount on the settlement was given to me on the 3rd and it gave me 7 days to settle!!!