Harassment of Telkom SOC of Loyal Customers

I have been a loyal customer of Telkom for over 20 years. I settled my account on time consistently. Lately I have not received any invoices and using my judgement made payments in line with my monthly used. Telkom suddenly, without prior warning terminated my services and send me a letter from Nu-Debt threatening to blacklist me within 7 days. This for an outstanding amount of R647.12, whilst my annual account is over R8,500 per annum!! This is harassment of a loyal and dedicated customer. I have tried using their lousy mobile application and are not able to connect as the service is not available.