Time & Location - High data usage
I know this question is old, but I just found the the same happening for me.

First off, you can see when your location services are currently in use when a little North-East arrow appears on your status bar next to your battery.

One way to find out which apps are using location services, is to start closing apps one by one and checking when that arrow disappears.

A better way is to look at the Location Services settings Settings &gt; Privacy &gt; Location Services. Here you can see all the apps that have requested access to Location Services and also what permission they have been granted ("Never", "While Using" or "Always"). Best pay special attention to the apps that show "Always". This means they can use Location Services even when the app is not active. This screen will also show a purple North East arrow next to apps that are actively using Location Services right now.

If you don't want the offending apps to have access to Location Services you can change their access to "Never" or "While Using" to limit the damage. Note though that depending on the apps purpose it might stop performing as desired.