Harassed for years over non-existent 'outstanding balance'

Though we loved DSTV as an entertainment platform, 2 or 3 years ago we decided to cancel our subscription and since then we have received calls every few months claiming that we still owe R400 on our account, which is false. We have contacted the billing department and have confirmed with them that there is no fee due on the account but yet, we still get called by DSTV claiming that we owe them money every few months.

We have tried everything we can to get off this stupid call list to no avail and now it has just become harassment. I have no other option than to post on here with the hope that it can get escalated and we can finally get removed from this call list.