HTC Wildfire help please

I just got my HTC, and I used wi-fi a couple times on it, but I'm still getting charged for data use. I turned off all data options on my phone. Why am I being charged?? This really makes me mad, since the person who sold me the phone said I don't need a data plan for this phone, cause it can work fine without it. Then why am I being charged?
Also I was sent a text saying I have a few days of free trial data usage unlimited. So I thought I would try it out. Went on the Android market, and downloaded a few apps. Now it shows I have more data used. Gahh I am so confused.
Please help I've never had a smartphone before.

Also since when does the phone's radio use internet to work?? Cause that's the only thing I used, but got charged usage.

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If you're using a radio app, like pandora, then it is not using real radio frequency, but the data connection.

There may be some other apps that are using the data connection too

No, I'm just using the radio that comes with the phone. It says I need to plug in my headset for an antenna, so I assumed it doesn't run off of data.