Select online/Nedbank debt collectors. ****mers

I made a call to get my remaining balance, and was sent an sms of a settlement amount on the 29th of October of the amount R2021 on my credit card, of which I settled on the same day and was told I'd get a payed up letter after the payment. I have been trying to get payed up later since and have been speaking to lady named Zuraida who is still trying to get more money out of me even though I keep telling her about the call and sms I recieved of the settlement amount. She keeps referring to a lady named Mitchell who I spoke to, who seems to never be around when I call. I now recieved an sms from the same company "select online" referring to an amount I need to pay and when I asked Zuraida about it she denies any sms being sent from the company.