Disable Apple's Wifi Assist in iOS9
While Apple's new iOS9 has some great new features, one specific feature might not make you so happy when your bill comes in. A new feature called Wi-Fi Assist is enabled by default, which sounds innocent enough until you realize what it actually does. If your WiFi signal isn't strong enough, it will start to use your mobile data.
Now you may think that unlimited data plans are the norm these days, but in many areas, including Canada, some Data plans can be quite expensive, especially if you are on an older contract/plan. So if the system is switching to your data without your knowledge, you could end up with a large bill at the end of the month.
Luckily, it's an easy fix. Simply open your Settings and navigate to Cellular. Scroll down to the bottom of the page and switch the Wi-Fi Assist toggle to off. Simple as that! Enjoy your Wifi only data! For more information, check out Apple's Support page on the subject.