I haven't had this problem with the characters that have passed Moria and Lothlorien, but I've had quite similar problems with the second character I leveled in Rohan, like an NPC not appearing, or an NPC being stuck in the middle of a quest. Unfortunately, the only guaranteed solution to this problem is to cancel the quest, and do it all over again. In addition to the lost progress, you will be also on a five-minute cooldown, but the only other way to do it is to wait a game master to help. Thus, you will have to weigh in which will be longer - a game master to respond, or to restart the quest.
Violence is the last refuge of the incompetent.