ㄴ다고 그러다

says that — casual reported speech

Reports what somebody said, with 그러다 standing in for 하다 the way speakers do. It very often passes on a rule or a warning: 이 지폐를 훼손하면 안 된다고 그러더라고요 'they said you mustn't deface their currency', 자꾸 말도 안 된다고 그러시는데요. It also holds someone to what they said before — 우리 플렉스한다고 그러지 않았어요? 'didn't we say we were going to flex?' 다고 하다 is the same content in neutral register; 그러다 is what you hear in talk.

Register: casual speech