MTN Refuses to Reverse Incorrect Charges

I contacted MTN on the 29th of January to cancel my contract at the end of February as this would be the end of the 24 month contract. I later sent an email to MTN customer care double check because I like to have email proof of my cancellation requisition. Busisiwe Mahlatsi confirmed with me that my contract would be cancelled at the end of the month as per my telephone request. However, according to another consultant I spoke to a few days ago, there was a technical issue and my contract wasn't cancelled at the end of the month. Therefore, on the 1st of March there were data charges amounting to R3200 on my account. MTN have also charged me the R350 subscription charge each month since then. I have now spoken Mmpo Mafikeng who is the retention officer at MTN and he refuses to reverse the charges, saying that they are legitimate charges even though the contract was supposed to have been cancelled. I've never heard of such a thing.