Mobile data
When I enable data for an app it automatically turns off data for that app, this doesn't to new apps that I install weirdly so I know it's not to do with how much data I have on my account
iPhone SE, iOS 12
Try first to optimize the range of the mobile network, see this Apple article:
If you see No Service, Searching, or SOS on your iPhone or iPad
If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support
See the following Apple articles:
Connect to Wi-Fi on your iPhone, iPad, or iPod touch
Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
If your iPhone or iPad won't connect to a Wi-Fi network - Apple Support
Check the router settings, Recommended settings for Wi-Fi routers and access points
Recommended settings for Wi-Fi routers and access points - Apple Support
Low Power Mode is On.
Charge the iPhone & wait until the battery is fully charged (100%).
The Low Power Mode will turned off automatically.