[BUG showstopper] Theft of ivory Mastodon still doesn't drop Tusks quest item

I'm stuck and cannot progress in the game. I've killed the Mastodon 5 times already and still it's bugged! no Tusks drop!

I did the following workarounds and still does NOT work, no tusks drop:
-Killed mastodon 3 times in middle of map
-Killed the mastodon 1st and handler second
-Gathered all the other items and then killed mastodon again in center of map

Right now i simply cannot make any progress due to this bugged main quest.

Any help would be appreciated.