Are you sure you've completed the "fire" aspect of the Badge? I only ask because we are not aware of this Badge being Bugged and that was the most common Help response from the Devs....that the person thought they fought 100 of both but really missed just 1 or 2 fires. Once they went back and got the extra Fires, the Badge was awarded.
*Edit, ok nevermind, I'm guessing there's divided tracking on this Badge where it shows you the count for both items involved...sorry, I haven't been in-game in a while so didn't know. Still, the Badge is not bugged as far as we know. Fight just a few more Fires and Hellions and if nothing triggers, send a Help Ticket in to the Devs.