2gb 24month modem plan

I was sold the modem as a free 24 monthly plan on top of my current contract by Rewards, a company who is contracted by vodacom to gather clients. The modem never worked with the signal in my area so I tried to cancel it. I also learnt from looking at my monthly statement that I was in fact being billed for the contract. I follow up with vodacom and they direct me to Rewards as Vodacom explained that it's my prerogative to investigate the allegation of mismarketting. I do so and rewards runs a investigation on the calls which sold me the product, learning that I was in fact misinformed and that I could cancel the contract with vodacom without a penalty. Today, 6months later, I'm still being charged for the modem and I followed up with both rewards and vodacom on the same story, a case that was considered closed. I am owed for over a years worth of charges for a faulty modem that was sold to me as a free product.