Unable to stop extra contract for device

Vodacom gave my contact, account, and current data usage detail to an external sales company.<br> This company phoned and offered me a cheaper extra data device, they said they see I use high amounts of data on my current MyMeg500 package with Vodacom. I agreed to buy this extra device, since I thought they represent Vodacom.<br> When I got the extra ****le, 22 May 2015, I took the unopened box straight to Vodacom office in Brooklyn, and asked them