Worst Possible service and arrogance

My wife took out a cellphone contract with Telkom mobile in July 2015 , there was no reception in our area so we returned the phone within the 7 day return period. Telkom sent out technicians twice to verify and the technicians agreed that there is no Telkom coverage in my area where I reside. Telkom has to date not cancelled the contract and they have billed us for the last 7 months. We have logged queries more than 20 times with the call centre staff (absolutely useless and arrogant). Finally today they cancelled the contract and reversed the charges of R2,408 but now they have now billed us a cancellation fee of R7,133 , for a phone we returned within the return policy. The call centre staff refuses to put me through to somebody senior to resolve the matter. Also my wife has been blacklisted for not paying for something she does not have. I NEED HELP !!!!