Telkom billing nightmare

I cancelled my Telkom WiFi contract February 2018 because I experienced constant network failures. Telkom confirmed a number of times that they received cancellation instruction but their accounting department kept on billing me. I obviously returned debit orders as my contract was cancelled. Phoning Telkom to fix their error did not help as they listed me at the credit bureaus and I received endless messages of final demand for payment. Not to mention the phone calls from Nudebt threatening me. Telkom must fix their mess once and for all and clear my credit record.