Telkom fails to contact me about a cancelled account for more than a year, then hands me over.

I cancelled my account in July of 2018, received confirmation that my account was cancelled and never heard from Telkom again. I thought I was one of the lucky ones. Now, a year later, I am being harassed by Debt-in who have said I am liable for covering a month's payment plus over R1000 in legal fees. Telkom failed to contact me themselves and this the first time I am hearing about the account. I have no problem paying the amount due, but I find it ridiculous that Telkom is not being held accountable for not contacting their customers when an account is outstanding. Instead, they let the account run-up for a year and then sell it to a debt company. Absolutely fuming. Debt-in says that Telkom can't contact their clients about an outstanding account because they have too many clients. That's nonsense - the system is automated to send out emails, there is a whole accounts department to follow up on accounts. I find it hard to believe that they're allowed to hand over an account to a debt collector when they failed to contact me for more than a year.