Vodacom: *****ently signed up to contract, cancelled within 5 days but still paying for it more than 1 year later

I was *****ently signed up to a vodacom contract by a call centre agent. She told me that as a valuable client they were reducing my data rates and would offer me a free wireless modem. I told her I already had a contract for a wireless modem and wouldn't need one. She rep**** it always good to have another one. I kept asking her so will my current billing for my vodacom cell contract + wifi modem contract be less with these reduced data rates. She said yet. At no point was I told that I was in fact signing up for a new contract. Only when the modem arrived did I realise that it was in fact a new contract. I immediately called Vodacom. I was told that it was no problem to cancel. All I had to do was return the modem and then call again to cancel. I did both of these things. This was September 2016. I have since called the Vodacom centre over 5 times. On two occassions I was told it was cancelled and I would get a confirmation of this through an sms and a reference number. In addition to the call centre I've gone into a store (guess what you have to call the call centre we can't help), I've raised a complaint via Facebook and via Twitter. I've also twice told call centre agents who have called me that I want this resolved. One hung up on me. I've been routinely billed and debited for this modem for over a year. I want to cancel this for good and I want to be reimbursed for all the money that I've paid - money that I'm paying for absolutely nothing!!!