False advertising and RUDE store managers

In January 2018, I upgraded and there was a promotion to only pay for 22 months instead of 24 months on the LG G6.

Last month, upon querying a different issue, it surfaced that I will actually pay the full 24 months and when I tried to correct this, I was told to go back to the store where I upgraded. I contacted the store and they told me different stories about the promotion (that the 22 months is only effective of you upgrade again). I reminded them of how they explained it to me when I asked in 2018 (they said it's the last two months of the 24 month contract that I would get free). It got to a point where I had to show them a copy of the catalogue from 2018 (because for some reason they couldn't find theirs). The store has since informed me that they have escalated my query to the head office. I did not receive any feedback after that.

I went into the store today and the store manager, Martin, was rather rude and started raising his voice at me, talking to me like I'm dumb. He didn't help me at all to be honest. For every question I asked, he just kept saying "I can't tell you that", clearly trying to get rid of me at any cost. They have not even bothered to provide me with a reference number that proves my issue was escalated.

All I am asking for is feedback because I believe I am approaching what was supposed to be the last month of my contract. I have heard horror stories about MTN not giving refunds where they are due and would hate for it to get there.