Samsung
Change Data Warning Limit auf Samsung
The data warning on Samsung phones sends a notification once your mobile data usage crosses a value you set yourself. It does not cut off your connection, which makes it different from the data limit that shuts mobile data off automatically once reached.
The default warning value is usually a rough estimate and often does not match the allowance in your actual mobile plan. If you keep it unchanged, you either get warned too early, while data is still plentiful, or too late, right before your plan runs out.
To adjust it, go to Tap on Settings ➔ Tap on Connections ➔ Tap on Data usage ➔ Tap on Billing cycle and data warning ➔ Tap on Data warning ➔ Set the Data warning limit and tap Set.
Set the value a few hundred MB below your actual monthly allowance so the notification still gives you time to react. If you want mobile data to switch off completely once a threshold is hit, use the data limit setting instead, since the warning alone will not stop usage.