Tortilla stole the fetish and took it to Balthazar to make a fake to replace it with, then later killed Balthazar, presumably
to keep him from telling anyone. According to the Tintin fanwiki, it isn't explained how Tortilla wound up with a fake fetish;
I'd assume Herge's intention was that Balthazar made 2 fakes and gave both to Tortilla, keeping the real one for himself.