Contract cancelation

I have been trying to call the mtn retentions department for close to 2months now and I hold for almost an hour without anyone answering. I want to cancel my contract that is due for upgrade because I don't want it anymore the installment that I am paying now is so much higher when I ask why I am told I have to cancel the contract if I don't want to upgrade it but the only department that can help me is retentions but they are not answering their phone it is really frustrating