HORRIBLE MTN

I did a premature upgrade in March of 2021. I was advised that I would need to pay penalty fees on which I agreed to. At the shop after i did the upgrade Masesi at the store said there's no amount due that's showing and it looks like that I don't need to pay the penalty fees. Month end came and I received my bill which was to my surprise over R 6000. I contacted Masesi and after a while she came back to me saying that MTN will pass credit on the amount and I don't need to pay it. We are already in June and NOTHING has been done since then. I have the emails where it's stated about the credit pass and also have a conversation from an agent where I received a reference number to pass the credit but STILL nothing has been done. Are there anyway this can be sorted?????