charges on a closed account

I paid off my absa credit card in august and closed the account. i went to the branch to do that, i also made sure i confirmed the account was closed by calling customer care. months later my account was debited by absa. i was called and told i was suppose to call so that they can delete the debit order. Today i open my emails and i receive a statement that i owe money on the account.How can i owe money on an account that i closed. this is causing a lot on inconvenient and frustration on me.can someone explain how come i owe money on an account that i closed?