
To check if your iPhone 7 Plus is using data, open up the Settings app, then tap Cellular. Look at the switch at the top of the screen next to Cellular Data.
If the switch is gray and shifted to the left, then your iPhone is not using data. If the switch is green and shifted to the right, then your iPhone is using data.

As you can see in the picture above, I have turned on Cellular Data on my iPhone. However, my iPhone is also connected to Wi-Fi. When your iPhone 7 Plus is connected to Wi-Fi, your iPhone won’t use data from your cellular plan.
This leads us into our first tip for when your iPhone 7 Plus is using a lot of data — connect to Wi-Fi whenever its available.
If a message gets stuck in the Outbox of the Mail app, it will keep using data as it tries over and over again to send. As this cycle drags on, your iPhone will slowly use up data.
If your emails continue to get stuck in Outbox, there may be an error in your email settings. To fix this problem:
If an app crashes, it may be stuck trying to send and receive data for a prolonged period of time. Usually, closing out of the app will solve this problem.
However, if this problem persists, there may be a software bug or issue within the app itself. If that’s the case, you may want to delete the app entirely and look for an alternative.
Streaming music and videos using apps such as Spotify, YouTube, or Netflix can be the biggest drains on your iPhone’s data. If you want to seriously cut back on how much data you use on your iPhone, only stream music and videos when you’re connected to Wi-Fi.
Let’s say you stream a lot of videos or music using the Safari app. You can turn off the ability to use Safari with data in the Settings app.
When you’re connected to Wi-Fi, your iPhone won’t use data. Therefore, make sure you connect to Wi-Fi whenever it’s available!
When you don’t close out of your apps, they stay loaded in the background so they’ll be ready to go as soon as you open them back up. Problems really begin when one of those apps you have open in the background crashes, which can make your iPhone battery drain fast and possibly cause other apps to malfunction as well.
Apps left on in the background of your iPhone can also still send and receive data, which may slowly drain the amount of data your iPhone can use.
If you’re ever wondering if an app is crashing on your iPhone, you can look for confirmation in the Settings app. Tap Privacy -> Analytics -> Analytics Data and check to see if any apps underneath LatestCrash. If there are any apps listed here, then there may be a problem with those apps which is making them crash.