A new feature in iOS9 is causing some unexpectedly large cell phone bills. WiFi Assist is, in theory, something that is supposed to make your internet browsing experience better. When you are experiencing slow, terrible, cafe wifi it will switch over to using your mobile carrier's data instead, so you can continue browsing without having to wait or experience long load times. The thing is, it doesn't really let you know it's doing this. If you are someone that has a data cap and this option constantly switches back over to mobile data, you may hit that data cap way quicker than expected.
Turn Off WiFi Assist
- Open up your "Settings" on your device
- Select "Cellular"
- Scroll down to the bottom and you should see "WiFi Assist"
- Slide it to the off position
It's as simple as that and could save you arguing with your mobile provider over the phone because "you should know better". Hope this helps!