Cancellation of contract as no service in area

I have been trying to get my contract cancelled for months as I have no signal in the berg. I have phoned, emailed, messaged constantly. Everyone I've dealt with has been polite and agree that it has been sent to the cancellations dept. Where is this ethereal cancellations dept. And why can't I speak to them directly. I am not paying for a service I can't use yet they continue trying to take money out of my account. I have even tried going to the shop in Durban I got the contract and wifi lte modem from, to return it, to no avail. I specifically went to a shop to find out what Internet service would work for me as I know the berg is not well covered. All I've got for my effort is months of frustration to cancel this contract that should never have been sold to me in the first place.