I don't know anything about using stored procedures.
However when you execute a prepared sql statement handle, you have to assign that result to a variable.
Does this help?

use strict;
use DBI;
use DBD::ODBC;
use Data::Dump qw(pp);


print "Trying to connect\n";

my $server_name = "XXXXXXXX";
my $server_port = 'NNNN';
my $database_name = 'XXXXX';
my $database_user = 'XX';
my $database_pass = 'XXXXX';
my $dbh = DBI->connect("dbi:ODBC:DSN=sql_test", $database_user, $datab
+ase_pass)
  || die "Couldn't open database: $DBI::errstr\n";
my $sql = $dbh->prepare("Exec sp_listUsers '25329601','1'") or die "ba
+d prepare $!";

my $results = $sql->execute();

pp $results;
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