Treating Customer unfairly

I bought a tablet for my son from Vodacom, contract, had the amount debited monthly from my account (R99.00). All of a sudden I noticed an additional number to my account, queried with Vodacom, Customer Services. The feedback I received was that it was due to some tele-sales which I then told Vodacom to cancel. I have never received any instrument nor utilized the number appearing on my statement. I was then assured that it has been cancelled and all charges reversed. Out of the blue I received a call from Vodacom Legal collections, I related the same story and sent all communication, they disappeared instead I keep on getting calls from different debt collectors which all the time I relate the sequence of events, they disappear with no feedback. It's been 3 years of trauma and torture, getting calls from different debt collectors handed over by Vodacom and every time I relate the same story, they promise to investigate and come back to me which they never do. I recently got a call from Alliance who also told me my account was handed over by Vodacom, threatening to black-list me, Alliance lady who was very rude, I had to tell her she doesn't have to speak to me like I am a ********, feeling helpless about the situation I told her to send me the details of where to pay this Vodacom accumulated amount for the unknown services to me, till to date, there's been no follow-up from either Alliance or Vodacom. PLEASE SOMEONE ASSISTS!