How do I stop uninstalled apps from using my cellular data?
The Cellular section of the Settings app on your iOS device is designed to inform you how much data you have used in a current period. The section includes a breakdown of usage by app, listed under your total current period usage. Sometimes "Uninstalled Apps" will be listed as part of your usage. Here's why:
Last month your carrier notified you that you are about to go over your cellular limit and they are glad to sell more for a trumped up price. You navigate to Settings > Cellular to see why you're using so much of your plan and notice that the Reddit app eats up a lot of data. To avoid paying for additional data you delete Reddit and a couple other apps to cut back on your usage. A few days later you check your usage again and see that "Uninstalled Apps" are at the top of your list. How are apps that you deleted still using data on your device?
They're not. The "Uninstalled Apps" category includes all the previous data from the apps that you deleted for that period. If the apps you deleted during a current period were not accounted for then the total data used for that period would not add up.
You can test this by checking the amount of data used by an app, then deleting it. Your "Uninstalled Apps" category should increase by the newly deleted apps usage.