Debt

I have a huge problem with cellc, 6 months ago my number was block for which reason I didn't understand. I tried to call I was told it was a billing problem but they blocked my contract number before they even billed me. I tried to call their call center to get an answer but as usual nothing. I then got a notice from my back saying was a debit order which was not allowed to ho throw because it was a huge amount. I realized it might be cellc. I gave them a call asking for a statement and of how much I owe . I was told I owe R12000 something in which I had spend on data. I was shocked and asked how was this possible because I can't spend that much money on data. I was then told I bought more than 200gb of data. I then asked why was my number blocked the lady did not have answers for me. I then received a letter from cell c saying I owe them R25288. Can someone please make me understand what is really going on here because every time I go to a cell c shop or call then I dont get answers. My contract was R200 per month, if I'm told I bought data for a mouth that his to this amount... How much data is that and what would I be doing with so much data. That amount of money there is my salary for 6 months. How is this possible that I owe R12000 then 25288? In a month. Please help me because this has affected my credit score big time. I need help and answers please