use strict;
use warnings;
use Data::Dumper;

my @months = qw/dummy jan feb mar apr may jun jul aug sep oct nov dec/;
my (%report,$cust,$value,$date);

while (<DATA>) {
  chomp;
  if (/^[A-Z]/) {
    $cust = $_;
    next;
  }
  ($date, $value) = split ' ',$_;
  my ($mon, $year) = split '/',$date;
  $report{$cust}[$mon] = $value;
}
print Dumper(\%report);

__DATA__
CUSTA
1/2015 100
10/2015 1,000
12/2015 1,000
CUSTB
2/2015 100
10/2015 1,000
12/2015 100