Why is my iphone 4 using my data when i have it turned off?

I have 150 MB of data for my iphone and i was exceeding that every month so i turned the data switch off and so I can only use internet at my house from our wi-fi but it is still exceeding 150?
Please help me figure out what I need to do differently so I stop getting charged so much every month for going over!
I thought that if you had wi-fi it didn't use cellular data?

Try turning off your imessage because that uses data

You are right, Wi-Fi doesn't use cellular data. There's really something seriously wrong, because I use data regularly on my phone and never even get up to 100MB. You should contact Apple or your carrier about this issue.

Try calling your carrier and slso help with my question!

This might help but try to double-click your home bottom and hold any app for a long time! Wait the the minus and quit them that's multitasking so it could be wasting your data all at once when you turn it on!

Data cell phones never turn off there data from internet. You can download data tracker and you will see that it never stops getting data internet. You should get sprint unlimited data because it would be better on your hands.