Poor service and unacceptable treatment

My 24 month contract came to an end and I was contacted by Mtn sales agents to ask me whether I would like to upgrade. I indicated that I was waiting for the release of the iPhone8 and iphoneX which was a month or two away and would prefer to wait. I was told that if I changed to a month to month contract with my own device I would save on the monthly premiums and I could upgrade my contract at anytime, which I did. I now have an opportunity to upgrade to the new iPhone and cannot do so as I am told that I need to wait until the full month for the contract is complete before I can do so. I phoned the call centre to resolve the problem, was then passed onto the Retentions department who then passed me on to the Corporate Call Centre ( ********** 325)department who did the sale to resolve. I got told the same story each time. I asked the agent in Corporate Call Centre that I would like to speak to someone senior and was put on hold and held on for 30 minutes with no response, resulting in me dropping the call. I believe that the agent did this deliberately. Breach of contract: I was told that I could upgrade a month to month contract at any time. This will be verified when Mtn listens to the call recording. Mtn is therefore in breach of its contract with me as they wil not allow me to upgrade when I want to. Poor service and treating customer with arrogance: I was put on hold for 30 minutes with no senior person picking up the call. That is putrid human behaviour and total arrogance.