More than 3 months of no response

I relocated to another country and no longer need my Nedbank accounts. Therefore, on 20 January 2021, I spoke to the Nedbank call centre and asked them to close my cheque account, savings account and credit card account. They assured me that my accounts will be closed promptly and someone will be in contact with me to pay or refund any final balances. They told me to remove any remaining funds from the accounts, which I did. They gave me a reference number ***7. I never heard back from them, and my accounts remained open. It's been more than 3 months.

Then on 1 April 2021, I received an email with subject "DEBTMAN eLetter -------***" stating: "You have used more funds than you had available in your account and this means you now have an excess balance. You have also not been responding to us. We therefore need you to make a deposit immediately to clear the excess and avoid legal action."

It turns out that the bank fees have continued to be deducted from the accounts in the more than 3 months that I've been waiting for them to close the accounts, resulting in a small negative balance.

This is unacceptable — their tardiness is now resulting in them threatening legal action? In what world does this make sense?