DSTV On Air - Worst Customer Service In History

I was called by a DSTV On Air consultant regarding buying a new decoder. As my older decoder was worn out I agreed. The agreement was that on top on my DSTV account they would debit an amount for 2 years. The 2 years has since passed and they are still debiting me every single month. They do not reply to emails, whatsapps and refuse to answer any calls. I want the recording where the sold me the product as I stipulated that they need to guarantee that the debit order will automatically stop to avoid the situation. I was given the guarantee and now I am completely hopeless and need assistance in exposing these people!