sudden data drain for Ipone 5s

I have an iphone 5 s. New from the factory March 2015. No facebook, utube or other downloaded apps on the phone. Use WIFI most of the time. Suddenly data usage went from a monthly amount of 2.25gb etc, to 7.85 gb last month. There were no changes in use. The phone sits on my desk all day rarely used. My phone said that I have used 2.83 GB of cellular data over the life of the phone.

I shut down almost all of the cellular data options and over the past 24 hours my phone said I used 5 mb. My cell phone company said it was 500mb.

Ive resorted to a reset / wipe but not confident that this will fix it.

Anyone else had this problem? And if so, what did you do.