thirst of all,

to the forum, take time and add info to your profile
second: screw the dealer, they are not supposed to charge you anything for repair under warranty (you said 2008 Sportage with less than 12000 miles, right?) So it still should be covered under 12/12 warranty, and even if not, 50/60 applies.
third - there are known issues (brake switch), ESC OFF switch...
and last thing - it may come on when you loose traction (skidding wheels, too hard turn and so on)
In other words, whenever you see the light to be on (flashing) while driving it means ESC was activated.