This is the 3128th most frequent Korean word.
갔다는
"갔다는" means "went" or "the fact that (someone) went."
'갔다는' is used here to report on heard information about someone's action of going.
그 사람은 한국에 갔다는 소식을 들었어요.
I heard the news that he went to Korea.
'갔다는' is used here to recount a statement about someone's past departure.
그는 이미 갔다는 얘기를 했어요.
He already mentioned that he went.
'갔다는' is used here to express disbelief about a confirmed fact regarding a past action.