Bill has a family plan with Verizon and one of his kids has been using up most of the data resulting in three overage charges. The problem is, he doesn't use it much. Leo says he'll need to look at the phone and see what it says. He should look at the cell usage in the settings. If it roughly matches, then there's something that the iPhone is doing that is burning up bandwidth. The good news is that he can look at the data usage by app in the iPhone's settings.
There are some things that will help keep his data usage low. For instance, Bill can turn off automatic updates in the App Store settings. Under cellular, there's a setting called "Use cellular data," and he can disable that for apps he doesn't want accessing data. He should also turn off location access for apps when not in use. When he's at home, he'll be able to still use those apps on WiFi.