Ugrading handsets under false pretences

About a month ago I received a call from Vodacom informing me that I'm due for an upgrade. I went ahead with the upgrade and thought everything went really well. I had my phone the next day. I ask the person several times if there would be additional costs on which I got a no. Today I looked at my bill and saw that I'm being charged for two handsets, I called the call centre and a very friendly lady informed me that there is a problem with the sales department not telling customers the truth. And that my contract actually only ends in March so I'll be paying for both handsets until then. I find this very disturbing. How can the telemarketer sell you something and not tell you the whole truth.