One Year and counting...

Feb 2017 I was ******, phone and computer ******. Reported to police - Insurance Claim submitted. In March I was told I had no insurance. I had to prove from my insurance that I did have insurance. MTN refused that my documentation was correct (the contract from them). Finally, in June, I was told that my insurance was correct and I was given a payout because they insured my computer for way too little. I cancelled both my telephone and computer contract. These were confirmed. I made my last payment to MTN in July. They kept on billing me until November 2017. All emails to their Customer Care email address, their Retentions Department, their Facebook Page, their shops and their hotlines, remained unsolved - their legal department provided with a wrong email to escalate it to on two different occasions. Now, I receive daily calls and sms's from a debt collector for their accounting mistake. Each time I ask for this to be resolved, I get promised it would be fixed, but it never does.