Telkom ruining my life due to their incompetence

I canceled my line in October last year as I would be relocated to another country for 10 months. In Telkom's utter incompetence they kept charging my account and to my surprise when I arrived back home I'm getting spammed by a company called NuDebt who Telkom has handed my account over to for debt collection.

Why did they keep charging my account after I canceled?

Why did they hand over a R2k debt without ever notifying me beforehand?

Your behaviour here is utterly reprehensible, you should be ashamed. I received no feedback from any inquiries I've made with you.

I will happily pay anything that was outstanding before I canceled. I will not however pay for your incompetence and I will take this as far as it needs to go.