Change the format in the CALL SYMPUT() to what you want it. Here you've specified date9, but I would recommend using yyyy.mm.dd which will sort correctly using ascending or descending.
call symputx('datenow', put(date()-1, yymmddp10.));
I also recommend changing to SYMPUTX which trims any extra spaces.
You also need to remove the single quotes in your outfile statement.
outfile="\\SharedFolder\REPORT_&datenow..xlsx"