Incorrect charges and no feedback for three months

I received a campaign call from Vodacom in February/March, informing me that data prices and call rates are decreasing and telling me that they would be upgrading my contract (for the remainder of my contract) free of charge. I double checked twice whether there was anything additional that I needed to pay, and was assured that my debit order amount would remain the same. I took up a contract that suited my needs, and DID NOT NEED A LARGER CONTRACT. If I thought I would need to pay more for it. I would not have taken it up. That months bill was R200 more than I expected. It turned out that they HAD charged me for the upgrade which I was promised would be no additional charge. I queried it in March as soon as I saw the bill. They promised it would be investigated. I was told that I had agreed pay more. But they refused to let me listen to the recording to prove it. They the. Transferred my query to an external provider. I have followed up multiple times, and have had absolutely no response. Eventually I called the Vodacom service Centre again. They tried four times to get hold of the external provider while I was on hold, and could not access them. How it is possible that the external provider does not respond to ANY of my emails, and that even the Vodacom call Centre can’t get hold of them. Absolutely ridiculous. And really pathetic customer service. I have been charged the incorrect fee for three months, and have been following up continually. This is completely disappointing. I truly can’t wait for my contract to expire so that I can move to another provider as quickly as possible. It is really unfortunate because the service of the internal Vodacom customer service Centre is brilliant. But the outsourced company is beyond useless.