How to disable port 21 for plain FTP?

I have removed PORT 21 from CSF at TCP_IN, TCP_OUT, TCP6_IN, and TCP6_OUT.
I have restarted CSF and LFD.
I have restarted pure ftpd service.

but when I tried to login to FTP with port 21, I can login successfully.
So, how can I totally disable PORT 21? I just want to use SFTP for security reason.

Thanks.

You can remove ports form csf/lfd, but Whitelisted IP(s) still can access those ports.

e.g. You would remove port 22 for SSH, but your Whitelisted IP will still be able to access it.
I recommend doing this to stop port sniffers and SSH access attempts.

is that mean that whiteliisted IP can access all ports in server although the ports have been remove from CSF/LFD? I'm not sure about that.
I have whiteisted an IP at my CWP server.Then I try to login to ssh via port 22, and it was refused, since port 22 has removed from CSF/LFD.
But it does not impact with PORT 21.
What's the difference?

Thanks.

when you ip is whitelisted you can access any port.