I'm using Wi-Fi at home and still being charged for data?

Iphone 4 and i have 3g and i tried to turn off cellular data, 3G and data roaming but AT@T continues to charge me for data when i use free Wi-Fi at home? Can somebody explain this to me and help me prevent this from continuing

Wi-Fi isn't free. Meanwhile, your iphone isn't using your Wi-Fi connection if you're still getting charged cellular data

You say: " i tried to turn off cellular data… "
So, it seems you did not turn off everything, or at least not properly. Check your iPhone manual or online instructions again…

Using your Wi-Fi at home, from your own home router should not show up as 3G usage. Now, if your home Wi-Fi is from some AT&T service (they are your home ISP also), they may have you "bundled" somehow with overall data usage, including home usage caps. However, home used Wi-Fi should not have any separate "data" charges.

Most smart phones will show a notification when they connect to any Wi-Fi. Check that you have notifications turned on, and watch what the phone connects to. Can't give any details, as I use a S3, which works perfectly switching from 3G to Wi-Fi anywhere…