Pokemon emerald video game help please how to get to mossdeep city?

ok i am kind of stuck, i all ready went to mt chimney and stop team magna , and went to metoriod fall and stop that plan 2... now am stuck.. it seems i cant go through 2 guys from team agua in shoal cave to go to mossdeep city, because they say i have to go to their hideout? what can i do ?