Terrible Service/Billing

I am so disgusted with Telkom service/billing. I had a Huawei router SmartInternet- 5GB Deal (24 months contract) of R149, 56 with Telkom. All of a sudden last month the bill escalated to R609.21 without my authority, when I query that call centre agent told me that I have increased the limit to R500 and she could not explain when and how. Which was off my surprise and she was very rude. She said I should cancel on the website if I want to. I also went to a branch they could not help. Moreover, this month it exceeded to R811, 91. In my right sense of mind, I have never spoken to anyone to increase the limit I am angry and disappointed with their terrible service and ripping me off daylight. Can they have the honesty to their clients?