#!/usr/bin/perl

use strict;
use warnings;

my $cust_file = <<'CUST';
200612:ABC
200905:DEF
200212:GHI
CUST

# create customer ID => name lookup table
my %cust_id2name;
open my $cust_fh, "<", \$cust_file or die $!;
while (<$cust_fh>) {
    chomp;
    my ($id, $name) = split /:/;
    $cust_id2name{$id} = $name;
}

# extract data from billing file
# and store indexed by customer name
my %report;
while (<DATA>) {
    my ($cust_id, $usage) = (split ' ')[0,-1];
    my ($switch) = /(SWITCH FastEthernet.*(?:IN|OUT))/;
    $switch =~ s/FastEthernet/Fa/;
    my $cust_name = $cust_id2name{$cust_id};

    push @{$report{$cust_name}}, "$switch $usage" unless $usage == 0;
}

# print report
for my $cust (sort keys %report) {
    print "CUSTOMER NAME:$cust\n";
    print "Device_Code Port Traf_Dir Data_Usage\n";
    print "$_\n" for @{$report{$cust}};
    print "\n";
}

__DATA__
200612 200612 SWITCH FastEthernet1_0_33 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 4.336 1.311
200612 200612 SWITCH FastEthernet1_0_33 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 35.435 10.716
200612 200612 SWITCH FastEthernet1_0_35 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 167.976 50.796
200612 200612 SWITCH FastEthernet1_0_35 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 26.064 7.882
200612 200612 SWITCH FastEthernet2_0_33 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 -0.000 -0.000
200612 200612 SWITCH FastEthernet2_0_33 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 -0.000 -0.000
200612 200612 SWITCH FastEthernet2_0_35 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 -0.000 -0.000
200612 200612 SWITCH FastEthernet2_0_35 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 -0.000 -0.000
200905 200905 SWITCH FastEthernet1_0_48 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 3.193 0.965
200905 200905 SWITCH FastEthernet1_0_48 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 41.499 12.549
200905 200905 SWITCH FastEthernet2_0_48 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 -0.000 -0.000
200905 200905 SWITCH FastEthernet2_0_48 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 -0.000 -0.000
200212 200212 SWITCH FastEthernet1_0_19 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 3.877 1.172
200212 200212 SWITCH FastEthernet1_0_19 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 0.837 0.253
200212 200212 SWITCH FastEthernet2_0_19 OUT 01-Feb-2010_02:00 01-Mar-2
+010_02:00 -0.000 -0.000
200212 200212 SWITCH FastEthernet2_0_19 IN 01-Feb-2010_02:00 01-Mar-20
+10_02:00 -0.000 -0.000
[download]

Output:

CUSTOMER NAME:ABC
Device_Code Port Traf_Dir Data_Usage
SWITCH Fa1_0_33 OUT 1.311
SWITCH Fa1_0_33 IN 10.716
SWITCH Fa1_0_35 OUT 50.796
SWITCH Fa1_0_35 IN 7.882

CUSTOMER NAME:DEF
Device_Code Port Traf_Dir Data_Usage
SWITCH Fa1_0_48 OUT 0.965
SWITCH Fa1_0_48 IN 12.549

CUSTOMER NAME:GHI
Device_Code Port Traf_Dir Data_Usage
SWITCH Fa1_0_19 OUT 1.172
SWITCH Fa1_0_19 IN 0.253
[download]

(Of course, you should open your original files instead of __DATA__, etc.)