Then how am I using a FTP client to connect through my SSH port if FTP is not enabled? What is the proper way to enable the FTP service and have a secure connection?
SFTP is a bad name for something that uses the SSH data channel to transfer files. Aside from being a tool for transferring file, it has nearly nothing in common with the underlying way FTP works.
If you want to control bandwidth on an SFTP session, you have to do it from the client side. So in filezilla, or whatever SFTP client you're using, you'll have to tell the client to control it's usage.
Otherwise, you'd have to put some sort of network level QoS in front of the SSH port.
Another way to do this would be to use RSYNC over SSH. rsync does have options to limit bandwidth, which you might be able to use, but you'd have to figure out the rsync command line options that work for yourself. I've never tried to control rsync's bandwidth use for that purpose.