How check daily data usage.

The only solution would be to reset your Cellular Statistics every day, which doesn't seem very convenient in my opinion. In Settings > Cellular scroll down to the very bottom and tap Reset Statistics.

To see how much cellular data you've used, go to Settings > Cellular or Settings > Mobile Data. If you're using an iPad, you may see Settings > Cellular Data instead. Scroll down to find out which apps are using cellular data.

Check the cellular data usage on your iPhone and iPad ...

If you find something is missing on iOS devices, you may provide --> Feedback - iPhone - Apple < here.