Unprofessional and ****mers

I made a payment arrangement to pay off fnb credit card. I paid it in full in February 2025. Its been 3 months and I still don't have a settlement letter and fnb is still charging interest. This company has the audacity to tell me to ask FNB for settlement letter when my arrangent was made through them I did however contact FNB and thet told me to speak to lawyers. This is ridiculous.