Hello To All..
The "Data usage warning" had been bugging me as well and I to have unlimited data until I changed something so very simple...
This is how;
1.tap on your notification bar and drag down.
2.tap on message "Data usage waring"
3.select "Set mobile data limit"
4.On the graph there are two horizontal lines one red"limit"and the other orange"warning", lift the limit line to the maxium of 100GB and also left the warning line to the same point.
5.tap "Set mobile data limit" and return to your home screen.
6.Now..Your notification bar should have freeeee and with NO data usage warning symbol.
Happy surfing..