Vodacom ***** agent

I have a contract with Vodacom. Which started at January I was paying R525 last month a Vodacom agent called me and told me that as a loyal customer they will reduce my payment to R519 and I will get more data n free minutes. To my surprise the debit order raised to R819 which is for the upgraded data n free minutes. I wrote an email to the Vodacom compliant email they never returned back to me until I went to the branch for cancelation of this upgrade. But because now I will start paying R539 because the discount I had from the beginning is already cancelled. I ask what will they do with the fact that a Vodacom agent is the one called me and **** to me and they said there's nothing they can do they can log a call to that department but cannot promise of they will call me. I've been with Vodacom for more than 15years using the same number I'm very dissatisfied and disappointed.