Failure to close my account causing me to have arrears

Good day

I hereby clearly express mu disatisfaction in your service. In the previous months I requested for my account to be closed and I received the confirmation that it is closed to my surprise I received a call on Friday stating that I am owing. I told them to send me an email of what I am owing as the account was closed and they didnt

The number that called me is this one +27 (79) ***. At which the person didnt deal with my case and told me to call customer service. How do I call the customer service when you confirmed the account is closed and whose cost for the errors you made.

Now currenty speaking my credit record is affected.