H1-B trouble

My H1-B application package arrived USCIS on 8/2, according to mail delivery track. On 8/29, I got rejection letter which indicated that there's no more available H1-B# for this year. But on 8/4 USCIS website shows that there still has 6,200 available #s. My mail got their office 2days earlier than 8/4. Why I still couldn't get any available #? Can anyone have any idea? Thanks a lot!