Telkom - incompetence to recon ADSL Account

Today I received a letter out of the blue from a Lawyer representing Telkom. In this letter it is claimed that I have an outstanding amount (monthly premium) for my ADSL line from April 2018!!!! I terminated this service at the end of May 2019. Each month for 4 years I paid. If an amount was missed due to overseas travel it rolled over to the next month (as any normal account does) and I would double the next month. Since May 2018 until May 2019, never did I see an outstanding amount due when I logged onto the Telkom site and paid via their Self Service facility. Each month was the monthly amount due. Even when I terminated my account, there was no correspondence that I had an outstanding amount. No letter in the post nothing!!! Because of Telkom's incompetence (no surprise there) I have had to pay an additional R501 for legal fees and interest. Shocking!!!! how the man in the street falls victim to incompetence of these companies.