Data Usage Menu

Is there a menu I can get to somehow on my phone that I am not seeing to review the data usage on my phone? I've recently been bit by Bell with a $450 bill for tethering my phone to my computer, and they offered to reduce it to $100 and I took it, paid it and forgot about it. But now this month they've charge me an additional $400 and are incredibly vague about why, citing that the data usage was high or something. Anyway, is there such a menu? This is the first phone I have ever had that I could not look at my data usage.

I should also point out that after getting my phone call from them warning me that they would cap my usage after $500, I stopped doing it all together, and they told me I had got up to i Bleive $483. How is it now I still owe them $400?