Samsung
Turn On/Off Data Warning auf Samsung
The data warning on Samsung phones is a separate function from the actual data limit. It only sends a notification once your tracked mobile data usage crosses a set threshold, by default 2 GB. It does not block data or affect your connection speed.
You manage it here: Settings ➔ Connections ➔ Data usage ➔ Billing cycle and data warning ➔ Set data warning. Toggle the switch to turn the alert on or off, or tap the value underneath to change the threshold to match your actual plan.
If the warning triggers too early, the saved threshold is probably lower than your real plan allowance. If it never appears, either the toggle is off or your billing cycle start date does not match your carrier's actual reset date, which throws off the usage count Android tracks for the current period.
Turning off the warning has no effect on billing. If you are regularly going over your plan, set a hard Data limit in the same menu instead, since that one can actually restrict mobile data once reached.