You are probably missing a slash at the end of the remote path:
"put C:\XXXX\XXX\filename.xlsx /xxx/xx/xxx/upload/" ^
See
https://winscp.net/eng/docs/scriptcommand_put#remarks
If that does not hep, we need a log file.
To generate the session log file, use
/log=path_to_log_file
command-line argument. Submit the log with your post as an attachment. Note that passwords and passphrases not stored in the log. You may want to remove other data you consider sensitive though, such as host names, IP addresses, account names or file names (unless they are relevant to the problem). If you do not want to post the log publicly, you can mark the attachment as private.
To delete the local file after upload, add the
-delete
switch:
https://winscp.net/eng/docs/scriptcommand_put#delete