Breach of contract and then over billed

I had a 2 year contract with MTN for a 3G ****le where i was paying R150 for 4Gig data on a monthly basis. The contract term elapsed and then i was told it becomes a month to month contract, which was fine because i was still paying R150 for the 4 gig. Somewhere between April and May the the 4gig was reduced to 2 and no one told me about it, that is where the problem started and since then ridiculous amounts have been debited from my bank account as follows:<br> <br> 2015-05-02 DEBIT TRANSFER MTN SP A******4 R 819.43-<br> 2015-06-01 DEBIT TRANSFER MTN SP A******1 R 321.04-<br> 2015-07-01 DEBIT TRANSFER MTN SP A******1 R 3,178.03-<br> <br> No one can explain how i got from paying R150 to the amounts above, I sent an email to customer service and i was told i had gone over my quota i.e. 2089.26 MB, meaning 89,26 MB over. I called the call center and i was told 1 MB over costs R0.99 so i needed to pay .99 * 89.26 = R88.3674 extra. So how did i get to being billed so much.<br> <br> I am not very happy about this, and as such MTN please rectify this nonsense and then refund me the cash