Account cancelled yet still received invoices.

We cancelled our Telkom account in May, giving a month notice for June, as we were leaving South Africa. I have a confirmation code for this. However, we are still receiving invoices each month and the deposit was never offset against the invoice. Have tried Telkom's chat service on the website to try get answers but you continuously get a message to hold for an agent. How does one actually get this resolved?! I don't want this affecting my credit rating!