my %files;

foreach my $CDR (@RECList) {
    my ($filename,$row)= split(/,/, $CDR);
    $files{ $filename } ||= []; # start with empty array
    push @{ $files{ $filename }}, $row; # append row to that array
};

# Now print out the data
for my $filename (sort keys %files) {
    open my $csv_fh, '>>', "/ClientRrecord/$filename.csv") or die "couldn't open [$filename.csv]\n".$!;
    print { $csv_fh } map { "$_\n" } @$row; # print out all lines (with newlines)
};