****mers!

I settled my ABSA Credit account in February 2024 after they gave me a settlement offer, i paid and they sent me a paid up letter . Few months later i got SMSes and calls from DMC that my account is in arrears, i told them the account was paid up and i sent the paid up letter from ABSA, they say they will escalate the issue and will contact me in a few days. They come back with a "resolution" that in their records i still owe ABSA and the account number in the paid up letter is different than the one in their records. My question is what do i owe them for because i have never been in contact with them? What and why do i owe them if the account was paid up and ABSA declared that?