i SPENT 1 month testing gathering, but in the end there was problem with router, which forwards ftp to my ftp server and another guy was responsible for that. So only today we solved FTp problem and decided to use proftpd.
Our firewall is ON, Selinux is ON. Everything works perfect.
the good idea if you want to test ftp server is to via terminal on ftp server do:
#give user anonymous#
and if you are in FTp server is fine.
no do that from outside
#give anonymous username
If it fails, problem with firewall, router, Selinux
If it works, You are Genius.
Try 3 times and if it still works, you can grab some good movie and relax for a 2 hours.