Sorry you’re having problems earning the trophy. That’s a known issue that our developers are looking into: Treasure Hunter Finish a Treasure Hunt with 2 or more Vaults - buggy? - #29 by killerman3333
As for the trophy, Customer Support has a point: Trophies are awarded by PSN, and since we don’t have control over PSN, we can’t award trophies at will. I won’t suggest you just try again, though. Instead, I’d suggest you wait until we’ve found a solution for this problem before attempting to earn the trophy.