If you never got the amulet, then apparently part of the quest was not updated properly, despite the speech option to the contrary, and the game is checking for the absent quest log update rather than the amulet in your inventory.
After paying to have the amulet duplicated, you should just have to wait a few minutes (real time) and talk to the jeweler again. He will open the conversation saying the work is done, and your only response is that you would bet nobody could tell it was a fake.
