A team aqua grunt standing in front of the last area entrance should have talked to you once you defeated the boss, you have to find the "sacred stone" first, once you find the sacred stone you should be able to speak again with a team aqua grunt to the entrance of mt summer, he will say you talk to the team aqua leader in kalijido cave(I dont remember the exact name :P), the leader will give you summer clothes, now you have to go to the mayor again and he will give you money and a hat.