I am being charged extra for the USB modemInternet

In January 2015 I purchased the Telkom Simple Package. Part of the package was that I would receive a USB modem and Internet starter pack. I was told to collect it from the Telkom store in Lakeside mall. I did try to collect it many times however they were always out of stock. On one occasion they took my contact details and said that they will phone me when the USB modems arrive in stock but they never contacted me. In May 2015 I went to the Telkom store and finally received the modem. I verified that I would not be charged for the the modem because it was part of the Simple package. Store personnel assured me that I would not be charged. However when I received my next bill i see that they charged me for the USB modem. I have raised an objection to this twice now and the problem is still note resolved. I am now receiving SMS stating that my account is in arrears and I will be cut off.