Incorrect charge

I have a top up contract with MTN. During the month of June I received one of those pop ups on the screen that says I have own data bundles. I won 3G of data. Now on my June statement I realized I was charged R262.28 and it says it's a charge for 3G data bundles. I called mtn because when I got this data it said I won the data. No where did it says I'm buying the data or would be charged for it. I spoke to 3 different people from mtn and all the time I'm told it will be sorted out. On the last call on 6 August 2015 I was told its a marketing problem, it will be investigated and the amount will be refunded on the next statement. The next statement came and the amount is still not reversed. Now I called today and the lady I spoke to says she cannot help me. This is so disappointing from mtn and it's day light *******. Being expected to pay for something you had previously been told you have won. Worse of all I'm on a top up contract so have never requested data or airtime from mtn. If my data or minutes finish I buy myself. Now I'm being charged for such. How can mtn charge me for something I did not request and have the decency to say they cannot help me.