Rewardsco Deception

I received a call from an agent saying they were from Vodacom and offered me an upgrade. They had all my contract details etc.

We discussed the new contract and the monthly payment and I agreed with the transaction.

I then received my statement and the amount was double what was discussed. When i contacted vodacom they said they never called me as it was one of their external sales companies called rewards co.

Now they say i am liable to pay for both handsets until my previous contract ends in July. This was never discussed with me by the agent at all and vodacom claims they are not responsible because it was not from them.

Paying for 2 handsets was never discussed with me, I was mislead and deceived by this rewardsco agent.

What's the resolution here?