Handed over to collection agency after cancellation of services

I have cancelled my Telkom account *** on 26.07.2019. Telkom has handed me over to a collection agency without my knowledge on the 19.02.2020. The collection agency is NAT300. Telkom can give me NO details about this agency. They are unlisted. The only info from Telkom is that I need to speak to this company to sort this out. Please could someone assist.