Hi Farhan
If the FTP port on ECC (DMZ --> ECC) can't be opened, can the port on PI (ECC --> DMZ) be opened? In that case you will have to place the file on PI system's filesystem and write FTP program on ECC system to go fetch the file.
The other option requires changing the system architecture. You migrate the PI system from DMZ to LAN. Inbound communication from outside the corporate FW first goes to Web Dispatcher in DMZ. The web dispatcher relays those calls to PI system in LAN.
regards