Threats to blacklist me without any prior communication

So my mother shows me an sms that you guys sent today threatening to blacklist me for an outstanding account that I am not aware of and you added extra fees too.

How can this be possible when you guys NEVER sent me ANY communication with a bill to pay neither did you CALL ME. I did not even know that there were outstanding fees. Then you give a reference on the sms only to find it’s linked to a Prudence Gumede who’s clearly not me so how can I trust that it’s really my bill? Worse you are using numbers that have been inactive for 15 years. How the heck is any of this my fault?

Kindly advise urgently as it is against the law and totally unacceptable to add fees or take any action to an account where you have not even communicated with the client.