Did some troubleshooting by starting the server from the command line.
Found that the reason it gives for the other ports not to work is:
error opening client socket! FATAL ERROR! Some other process is using this port!
So it is not the service provider's fault.
When I test with telnet, I find (after stopping shoutcast)
telnet stream.radiosai.org 8021
Connected to stream.radiosai.org.
Escape character is '^]'.
GET / HTTP/1.1
Yesterday when I tested, ports 8023, 24 and 25 were also probably occupied by the other process. Today, those ports were open, and shoutcast could use those ports.
Netstat -a -b -n -o > c:\netstatnames.txt
and searching for 8021 in that file,
found that the process is
So, requested that the Gene ftp be tweaked so that it uses only ports above 8100 for listening, like 8121 etc. That solved the issue.