Umm... What's that at the end ?

it's the money with SOS sign, the rescue team just send it back to dong-uk because they know it's his so they are not going to rescue him forever

Wrong! They mailed it to him bec he was looking for it in the earlier chapter after his rescue to make it as a souvenier. The police/rescuers did not consider that he may have needed help the second time bec who tf would go back to the site where they had an accident