Charging after account is closed!!!!!

I closed my account in March this year. Now on 12 March 2020 you send me a sms saying an outstanding amount must be paid. I have a letter from Gezina Branch staying that this account has been closed the positive amount was paid out to my ABSA account. No debit order is on this card. How can you charge fees after the account has been closed!! How can you transfer funds a positive amount to different account and then come and say funds are owed. I also send a letter in March about misleading or inconsistent information that is provided to me. Please explain what is happening. I have now attempted to phone FNB but I am send from one devotion to the other. It seems FNB has a small problem seeing that I do not have an account with them. PLEASE sort this out NOW!!!!