I partecipated in the promotion. I followed the procedure but when I loaded the proof of purchase something went wrong. I turned to the Samsung Call Center and I was told that everything was OK. Yesterday an e-mail tells me that not having recharged the documents by deadline my request has been canceled.
Moral of the story: don't trust the Samsung Call Center.
However, congratulations, you have sold a Note 9 promising to buy back a Note 8 and then the naive customer does not reload the documentation. So that's it.