PAID IN FULL BUT APPERENTLY STILL OWE MONEY

I have an over due account with absa, and I was handed over yes I paid my account in full without any discounts!!!!! I received a letter from them to say the account is settled but now I am getting messages saying I still owe them over R3000. I called numerous times and everytime I had to explain to these agents the same story! that the account is paid and that I need my letter from ABSA to say the account is closed but they don't help, they don't call they don't follow up. their service is unexplainably horrible. I HAVE PROOF OF ALL MY PAYMENTS AND A PRINT OUT FROM ABSA SAYING ITS CLOSED

how can i receive a paid in full letter then get another message saying i owe money????????????????????????????????