Shocking service, need help

First of all, I would like to state that I have been a loyal MTN customer for the past 15 years. On 4th of August 2017, I was invited by MTN to upgrade my existing contract. After upgrading and activating the new contract, I was promised that I would receive my phone within 5 working days. After numerous phone calls, emails and even visiting their Tygervalley store, I still didn't have my phone after two months. In desperation I then decided to cancel my contract since they had no intention of honouring their side of the contarct (after I've been paying for my new contract for 4 months already). Needless to say another two months went past and they still can't manage to cancel the contract. Despite my request to speak to management, they keep denying access. Where can I go, for someone to help me finally cancel this contract? I have details of people that I spoke to and the dates that I spoke to them, if needed.