Given a device that does not work

took out contract with MWEB in July 2015 for Wi-Fi Router which was delivered on July 16th and I immediately found out that it wasn't working. I contacted them and they told me to take to Cell C store where they confirmed it to faulty( manufacture technician) and I gave MWEB a feedback and they said they would replace it but to date they haven't. They sent me an SMS saying they are out of stock but when I called them saying its 40 days into the contract and I'm sitting with a device that doesn't work and they are saying I must bring it to their store for exchange after I've paid for delivery for already. I've paid over R500 already for connection and delivery.This is a 24 month contract of which in the 40 days I'm paying for an imaginary service and what frustrates me the most is the automated emails each time I email them saying 1 of their agents would call back but it never happens. I want out of this contract because they haven't given me any service and I want to be refunded because they haven't given me anything and I should not have to pay any cancellation fees because I am not at fault.