Telkom blacklist without valid reason

Received an invoice and statement advising that an amount due will be debited to my account on 25 Jan. I forgot about it as it was confirmed that it would be debited. Next thing Investec tells me I have been blacklisted by Telkom. I received no notification from Telkom advising that they couldn’t process the debit order! How about asking me for payment before just blacklisting. I think this is an opportunity for legal action!!