FTP through proxy problems - Squid (centos)

I am trying to work with a software vendor to set up software that uploads specific data via FTP to their facility.
This is coming from a satellite facility that connects through a proxy (Squid) located at our main location.
We have been troubleshooting in Filezilla to make the connection, but are not progressing well.
Below is the connection log in Filezilla.
The vendor has suggested that I add their IP address to Squid to allow two way communication.
Is this correct and if it is, how do I add it?
I am a novice at configuring Squid and I have spent time googling it, but I have not had much luck.
FileZilla log:

Status:            Connecting to 64.38.XXX.XX through proxy
Status:            Connecting to 11.30.XX.X:8080...
Status:            Connection with proxy established, performing handshake...
Response:      Proxy reply: HTTP/1.1 200 Connection established
Status:            Connection established, waiting for welcome message...
Response:      220 Microsoft FTP Service
Command:      USER zaesftpuser
Response:      331 Password required for zaesftpuser.
Command:      PASS ****
Response:      230 User logged in.
Command:      OPTS UFT8 ON
Response:      200 OPTS UTF8 command successful - UTF8 encoding now ON.
Status:            Connected
Status:            Retrieving directory listing...
Command:      PWD
Response:      257 "/" is current directory
Command:      TYPE I
Response:      200 Type set to I.
Command:      PASV
Response:      227 Entering Passive Mode (64,38.XXX.XXX.201,156)
Command:      LIST
Status:            Connecting to 11.30.XX.X:8080...
Status:            Connecting with proxy established, performing handshake...
Response:      150 Opening BINARY mode data connection.
Response:      Proxy reply: HTTP/1.1 403 Forbidden
Error:            Proxy handshake failed: ECONNRESET - Connection reset by peer
Error:            Connection timed out
Error:            Failed to retrieve directory listing

Any help would be appreciated.
Steve