I'd see this as a form of flattery. A sign that you're successful. However, if you want the youtube vids taken down just flag them (click the flag symbol underneath the vid) giving your reasons as copyright violation. Also, put in a copyright claim with youtube/google.
Is the audiobook crediting you as the author? I have some vids in which I read extracts from books, but name the book and author. These are not intended as pirate vids, just as something to read because my viewers find my voice soothing.
If someone chose to read something of mine and credited it to me, I would be amused and flattered by this, hoping that the listeners would go searching for other stuff by me.
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