I have one FTP account for customers and I want they upload files, but they should not see what already uploaded by other customers.
Is that possible?
If I will disaalow directory listing that will "break" frp connection.
No, this is not how the FTP-Protocol works. If you don't want customers to see the files from one another, create multiple users.
I've done that with Filezilla server on Windows. Give the upload directory write but no read permission and they can upload but not download (including not retrieving a directory list). The only side effect is they get an error in the FTP client when they connect and after they upload. FTP clients try to pull listings after both events.