Have you turned of the internet connection on your I phone?
Settings > General > Mobile Data > Mobile Data Network and then turn off Mobile Data.
Also if internet connection not disabled then usage can be for emails, Apps updates etc.
Xiaomi Mi Mix 2 review
See mcbess's iconic style animated for Mercedes-Benz
iPhone X news: Release date, price, new features & specs
Black Friday 2017 : date, sites participants & bonnes affaires