Thank you for the opportunity to help you with your question! I shall do my best to help you out!
Hello! I am only familiar of how to do this for Windows (so I apologize in advance if you have a Mac, as I am unsure how to block FTP with those).
You would go to your start menu and click on "run". You will notice the appearance of a new small window on the screen. In
the text field of this window you need to type "cmd" and then press the
"enter" key. A new window should open which is usually called the "command prompt" or "MS-DOS prompt". On my computer is comes out as "command prompt", but on the new computers, "MS DOS prompt" is what it is called.
To block FTP you would type in that box: "telenet my-domain-name.com #" (number of the FTP server you are trying to block). That's what I did on mine and it works. I hope it proves useful to you!
Please let me know if you need any clarification. I'm always happy to answer your questions. Thank you very much!