NFL Mobile App used 18GB background data??

I had an unprecedented background data drain last night while I was sleeping - on its own, my NFL Mobile App somehow used over 18GB of data while minimized, phone asleep and locked.

This is a trusted app I've been using for at least 3 years without any issues. I do not use it to watch videos or live streams, only to get updated game scores.

Of course I have resolved the $150 coverage fees, and uninstalled the app. Has anyone else seen anything like this before (me, never)? Ideas? Preventions?

(BaTW, AT&T CS and Tech support were fantastic!)