Problems with Anzu's quest chain

Good afternoon!!
I wanted to report a misfortune I unfortunately had with the Raven Lord quest chain. When I reached mission 11, the whistle that would allow me to continue the quest disappeared. I spoke to a GM of the game, but unfortunately, he couldn't help me! What do you recommend, or is there a possibility a GM could help me with this? I wouldn't mind doing them again if necessary.
Thank you for your time.

try go back previous NPC ?

Quote:

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Defeat the Guardian of the Eagle and obtain the Essence of the Eagle. Use Arthorn's Sparrowhawk Whistle to call Arthorn's Sparrowhawk to relay news of your success.

If you lose Arthorn's Sparrowhawk Whistle, return to Arthorn Windsong at the Evergrove for a replacement.

[Essence of the Eagle]
[Arthorn's Sparrowhawk Whistle] (provided)

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