Been asking for a Paid up letter

I was offered a settlement on my Standard Bank credit card in March 2021 which I paid in March 2021 but in April 2021 I received calls the whole month saying I have an outstanding balance I told told all of them I want a Paid up letter they told me they can see the money i paid I don't even have to send proof they will escalate the matter to their supervisor untill today every morning after 7am I get a call from MBD it's been 3 months since I have settled my account and it's been three months of harassment why offer us a settlement amount if they going to say we still owing can someone help if I'm not getting help I'll have to report this matter to council of debt collectors02