Being double billed since August 2015 with no help

I signed a contract in August for a lte modem for R399 pm. I am being billed R699 pm even now after speaking to about 30 consultants, I am in the same place as I started. I keep getting transferred and promised someone in the right department can help. Still waiting and still no results. Going back to telkom was the biggest mistake as you cannot walk into any store or shop to just fix this. All has to be telephonic which allows Telkom to do nothing.