First, did you complete all of the Torga quests? I can’t remember off the top of my head if it will let you do the Frog chain without completing it, but I’m just throwing it out there.
It that’s not it, check a bit further down the quest chain for the goblin stuff. It’s not that hard to do the first couple quests for it while doing the frog stuff and not realizing it.
Try tracing through the quest chain to see if you can find a quest to pick up: