If you’re running iOS 9 on your phone and your data rates are more than they were before, a feature called “Wi-Fi Assist” could be to blame. It automatically allows your phone to download data via your cellular plan when Wi-Fi coverage isn’t great. That means the data will keep downloading at slower rates and running up your bill.
Here’s how to turn it off:
1. Go to Settings.
2. Click on Cellular.
3. Hidden all the way at the bottom of the list of app you use cellular data for is “Wi-Fi Assist”
3. Simply toggle this option off.