Try toggling Airplane Mode on and the off again and see if it helps.
If not try Settings-General-Reset and reset all settings.
After that a forced restart for your model.
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support
Try toggling Airplane Mode on and the off again and see if it helps.
If not try Settings-General-Reset and reset all settings.
After that a forced restart for your model.
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support
If you have restrictions enabled, check:
Settings>General>Restrictions>scroll down to Cellular Data... and allow
Regards
Giulio
Data turning off when exiting settings