FTP control channel is on port 21, data is on 20 (for active ftp).  SFTP
uses the SSH daemon, so runs on port 22.

It has been my experience that the pure-ftpd init script is far from
graceful, as Eric pointed out, the error that was given likely means that
the service wasn't running.  That, or it just couldn't find the pid file.

lsof -i :21 will tell you the process (with pid) that is listening on port
21.  You can then kill that process.  Provided you have also used chkconfig
to disable the service on startup, it will then effectively be stopped from
running.  The rpm -e or yum remove commands listed above will make doubly
sure that the service won't be started up again on the server.
 Additionally, you could use iptables to disable any connection to port 21
on the server :
/sbin/iptables -A INPUT -p tcp --dport 21 -j REJECT

I think that should stop incoming connections on the port.

-- Dan.