Forced to pay Unwanted product

I was contacted on the 7th August 2015 by Siyakhula Products (Mr Steve Kumalo) regarding short delivery of black ink cartridge on my old order which was already delivered and paid for. I had received the delivery for my short order on Monday the 17th August 2015 with an invoice. To my bewilderment the invoice that I had received, I had phoned Siyakhula Products on the 19th August 2015 to ask why I was being invoiced on a product that they had said was a back order. I had also requested that they should send me the voice recording for the last conversation that I had with them about the back order, as well as the current voice recording that was taking place, however they were unable to send it to me. Moreover, I had requested for their physical address in-order for me to return the unwanted product, and they stated that it was not possible and they refused to give me their physical address. I want them to come and collect their unwanted product as well as delete us from their system.