Treasure Hunter collection unlock
In your shoes, I’d submit a new ticket (referencing the old one) and ask for it to be escalated to a higher-level Customer Service member. Regardless of why it didn’t unlock for you, you do have the item and the collection system should acknowledge that. I believe that CS has managed to adjust that for others who hit various bugs.
Good luck and please let us know how it turns out (so we can help the next person with a similar issue).
John Smith: “you should kill monsters, because killing monsters is awesome.”