Exorbitant charges for cancellation

I upgraded my contact with Telkom mobile on the advise that they had coverage at my new address. After 8 months of paying for the contact and fighting with them to get technicians out. The last technician that came out to install an antenna advised that there was no coverage and he was going to recommend the cancellation of my contract. I have now been advised that they will cancel my contract, but I must pay R 1 769.60 for the devise, which I have been unable to use and would happily return. The cash price for this devise if bought outright is R 1 750. So after 8 months of paying for my contract they are wanting to charge me MORE than the cost of the device to cancel. In my mind I should be refunded for the contact I have paid for up till now as I was miss advised that there was coverage at my address. All I want is for them to take back their devise and cancel my contact!