Useless telkom

I have a huge concern with Telkom. Last year I cancelled my adsl account and paid the last invoice as required but telkom continued to bill me for 3 months even after they called me to confirm the account was closed. In Jan 2019 i get a call from a lawyer advising me that i was blacklisted.

Telkom is refusing to resolve this matter.

I will appreciate it if you can get anyone in management to assist me to resolve this issie