TELKOM NGN - I do not want this on my credit record. make it stop

I have cancelled my Telkom account ages ago but I still receive an invoice. I could live with the invoice, but now something called TELKOM NGN is showing up on my credit report and I do not appreciate that at all as I am trying to have a clean credit record.

I have tried resending the cancellation forms to stop the invoices, and nothing has happened.

Today I used the chat function and the person helping me was no help at all. Was very inconsiderate and ready to dismiss me without any compassion.

I am fed up with this