Connection Refused on Mac via FTP

I have MAC OSX 10.9.5 and I'm new to FTP connection on Mac. I couldn't find a clear list of reasons that I cannot connect to a server. The server is running but when I try to connect through FileZilla, command line ftp, or finder ftp I get an error that says 'Connection Refused'. I didn't get this error a few days ago when I tried to connect so what could have been changed?