Telkom blacklists existing paid up customer

I have both a cellphone as well as a fiber contract with Telkom. All accounts is paid by means of a debit order generated by Telkom.

A while ago some lawyer firm Hugo & Ngwenya attorneys contacted me and said that I owe Telkom an amount of R1256.92. I have no other account with Telkom. I requested them to send me the details of this claim. I want to know where does this claim comes from. I made several requests in this regard. To date I have received nothing. Yesterday I received an sms that I have now been blacklisted on some credit bureau. And I must call ********** 668 quote reference ND ********** 7

To my knowledge I do not owe Telkom a sent and unless they can deliver proof that this is a valid amount that I owe, I will not pay them. Why do I have to go through all the pain to get this false claim removed from my name.