The mobile data screen is even there when I go Into it. All it says is "an update is required to use mobile data on this phone" learn more.
@lfcheart that suggests that your phone requires an update from the manufacturer.
I think, up-thread, you mentioned Apple, so it is an iPhone.
Connect to a PC and sync with iTunes to see if that prompts the update to be downloaded. If it were an Android, I would connect to WiFi and check, via settings, for an update.
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor