Hidden processes causing huge increase in ios data usage?
I have this too. 100s on MB per Day. AT&amp;T carrier.  Started a few months ago. In 20-50mb chunks and lady week ramped up into the 100s.

In cellular usage Stats none of the apps were displayed. Cellular data was listed as zero.  Not GBs!  

Restored the phone from an image backup. Nothing changed. Bit the bullet and  Restored as "new".  Fixed.  Had to reinstall everything 

Something infiltrated my phone and wax using it.  Apple won't talk about this at all