Why was the game annulled?

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TalStyleGame
Dear chess-loving friends, I played a 3-day game on Chess.com and checkmated my opponent. After I checkmated them, the game was annulled. Before the game started, my ELO was 400, but even after the game ended, my rating didn’t change — it didn’t go up to 1000. Why was the game annulled?
justbefair

Looks like the game you finished today was rated.