Can't make SIM800L +FTPSIZE work for me

Hi, I am uploading an image file to FTP using AT commands.
Sometimes the file arrives missing a part and also the size of the image is smaller than the original.
I would like to check and upload again as required so I need to check file size after upload.

When I run +FTPSIZE it responds OK but +FTPSIZE: 1,61,0
what means filesize = zero what does not correspond to the real file size.

  sendATcommand("AT+SAPBR=2,1", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPCID=1", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPSERV=\"ftp.mysite.com\"", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPUN=\"user@iot.mysite.com\"", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPPW=\"mypass\"", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPGETNAME=\"200504121334.jpg\"", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPGETPATH=\"/\"", "OK", "ERROR", shortDelay);
  sendATcommand("AT+FTPSIZE", "OK", "ERROR", mediumDelay);

Thanks in advance
Paulo