ABSA collection agent harassing me for a CLOSED ABSA ACCOUNT!!

In March 2022 I had A FULL FINANCIAL CREDIT INVESTIGATION with ABSA staff and ABSA management. At this time, ABSA closed ALL MY ACCOUNTS, and supp**** me with letters indicating that these accounts have all been closed and settled. However, I am being harassed by MBD, which is apparently "collecting" for ABSA on an account "sold" to them. How is it possible that I have a letter (and a how bundle of emails and correspondence from the 2022 investigation) yet they still harass me for money? How can ABSA sell an account that they closed and issued a letter for? Trying to get assistance from ABSA on this, but it is not very successful. ABSA have confirmed in writing and verbally (call on Tuesday 13 Febr 2024 with Alpeus M at ABSA) that this specific account is CLOSED!!