About a Finished Dungeon

This is seriously absurd... Shouldn't I be rewarded for completing it before the dungeon ended? Why don't they give me the gems after the dungeon closes... I cleared the level a few days before the dungeon ended, so I was waiting, thinking they'd give it to me... It's truly baffling that they won't give it to me because it's over now... And even though it's a different game, every time I cleared a location, they sent me messages like, 'Mission rewards that have been normally achieved can be claimed all at once on the dungeon screen after defeating monsters.' But now they're saying it's difficult to provide rewards for ended dungeons...