Many times it so happens that the pure-ftpd service doesn’t work with CallUploadScript set to yes in the /etc/pure-ftpd.conf file.
That is because the pure-uploadscript service is not getting started while restarting the pure-ftpd service and hence you will have to manually restart pure-uploadscript for the FTP to work.
You can apply the below simple fix for it ::
Firstly restart the pure-ftpd service
/usr/sbin/pure-uploadscript -B -r /etc/pure-ftpd.conf
Now telnet IP 21 works fine and so does pure-ftpd service.