Telkom account handed supposedly over for Debt Collection - Telkom never liaised with the client at all!

I cancelled my Telkom line on 31 Aug 2017. I recently have been harassed by a Debt Collection agency who want personal details before they even reveal who they are and what the call is about. I received an email from them today threatening that I be handed over for "possible legal action". I have yet to be informed of an amount that I supposedly owe, so it not possible that I could have refused to make any payment.

TELKOM, you had all our paperwork sent to you, and you have personal details, so I expect that you call and/or email me to stop this harassing, and to try and amend an already poor reputation in some way.