Unwarranted threat from Nedbank - Credit card that was closed in November 2023

I closed my credit card with Nedbank in November 2023. Today the 9th of April 2024, I received an SMS threatening to take legal action against me and ruin my credit record. I called and all three consultants from Nedbank confirm that my credit card is closed and they cannot see anything. I want to understand a) why did I receive the sms b) confirmation that indeed I do not owe Nedbank anything. Please note that I have an email 3 November 2023 confirming that my credit card was closed. You have not attempted to get hold of me for any monies owing. I have contacted your call centre several times for other matters and they always offer me a credit card which I decline all the time. Why am I now owing?