Utterly poor service

So my issue started in the beginning of March when I received a call from mtn retention department offering me an upgrade on one of my data contracts which included a mobile pocket router. I accepted their offer and I was promised delivery within 5 working days. We are now in the middle of July and still no delivery has taken place. I have sent numerous emails trying to cancel this contract with zero success. However my account has been debited each month for a devise and service that I have not received. Included with the devise I should have received a new sim card. This also never arrived. When I call the call centre I am transferred to their retention department who never answer the phone. I want this matter resolved but no one at mtn can assist me. I feel that the service received is utter appalling as I have not skipped one payment on this account although mtn has breached their side of the contract