If You Recently Updated your iPhone, you Need to Change this Setting Immediately
If you don't adjust this setting, you'll be using A LOT more data!
Have you upgraded your iPhone to iOS 10? If so, you'll want to go in to your settings and make sure "Wi-Fi Assist" is off. When you have this feature on and your wi-fi is spotty, it will start using your data...and that can REALLY add up!
When I got my new iPhone over the summer, I specifically remember turning this feature off. But when I upgraded to iOS 10, apparently it automatically turned this feature back on!!
If you've updated recently, do yourself a favor and check this. If it's on, you could be using a lot more data!!
Go to settings, then "cellular." Scroll all the way down, and make sure "Wi-Fi Assist" is to the left, and NOT green,