Closed account - now overdrawn

I closed an account, which was confirmed via email and a final bank statement with a R0 balance.

I am now receiving emails and SMS's from the bank saying this closed account is overdrawn.

I have contact the service relationship manager at the Lambton branch, as well as her manager at the EastGate branch. They have refused to give me the contact details for someone higher than the manager. I will now take this up with the banking ombudsman.