You only supplied 1 record in your example so it is impossible to see how the records are separated. However, this should be enough to create the hash with the keys and values you desire:

use strict;
use warnings;

use Data::Dumper;

my $data = do {local $/; <DATA>};

my %records = $data =~ m{^ACCOUNT NUMBER\s+(\d+)\s+(.*?\d\d/\d\d/\d\d\
+.)}msg;
print Dumper \%records;

__DATA__
ACCOUNT NUMBER    000111111111
YOUR LOAN PAYMENT FOR THE YEAR WILL BE 00.00
   OF WHICH 00.00  WILL BE FOR PRINCIPAL AND INTEREST,         00.00
   WILL GO ESCROW ACCOUNT, AND .00  WILL BE FOR
   DISCRETIONARY ITEMS THAT YOU
   CHOSE TO BE INCLUDED WITH YOUR LOAN PAYMENT. 
THE EFFECTIVE DATE OF YOUR NEW SCHEDULED PAYMENT IS 00/00/00.
ACCOUNT NUMBER    000222222222
YOUR LOAN PAYMENT FOR THE YEAR WILL BE 00.00
   OF WHICH 00.00  WILL BE FOR PRINCIPAL AND INTEREST,         00.00
   WILL GO ESCROW ACCOUNT, AND .00  WILL BE FOR
   DISCRETIONARY ITEMS THAT YOU
   CHOSE TO BE INCLUDED WITH YOUR LOAN PAYMENT. 
THE EFFECTIVE DATE OF YOUR NEW SCHEDULED PAYMENT IS 00/00/00.
ACCOUNT NUMBER    000333333333
YOUR LOAN PAYMENT FOR THE YEAR WILL BE 00.00
   OF WHICH 00.00  WILL BE FOR PRINCIPAL AND INTEREST,         00.00
   WILL GO ESCROW ACCOUNT, AND .00  WILL BE FOR
   DISCRETIONARY ITEMS THAT YOU
   CHOSE TO BE INCLUDED WITH YOUR LOAN PAYMENT. 
THE EFFECTIVE DATE OF YOUR NEW SCHEDULED PAYMENT IS 00/00/00.
[download]

Output:

$VAR1 = {
          '000111111111' => 'YOUR LOAN PAYMENT FOR THE YEAR WILL BE 00.00
   OF WHICH 00.00  WILL BE FOR PRINCIPAL AND INTEREST,         00.00
   WILL GO ESCROW ACCOUNT, AND .00  WILL BE FOR
   DISCRETIONARY ITEMS THAT YOU
   CHOSE TO BE INCLUDED WITH YOUR LOAN PAYMENT. 
THE EFFECTIVE DATE OF YOUR NEW SCHEDULED PAYMENT IS 00/00/00.',
          '000222222222' => 'YOUR LOAN PAYMENT FOR THE YEAR WILL BE 00.00
   OF WHICH 00.00  WILL BE FOR PRINCIPAL AND INTEREST,         00.00
   WILL GO ESCROW ACCOUNT, AND .00  WILL BE FOR
   DISCRETIONARY ITEMS THAT YOU
   CHOSE TO BE INCLUDED WITH YOUR LOAN PAYMENT. 
THE EFFECTIVE DATE OF YOUR NEW SCHEDULED PAYMENT IS 00/00/00.',
          '000333333333' => 'YOUR LOAN PAYMENT FOR THE YEAR WILL BE 00.00
   OF WHICH 00.00  WILL BE FOR PRINCIPAL AND INTEREST,         00.00
   WILL GO ESCROW ACCOUNT, AND .00  WILL BE FOR
   DISCRETIONARY ITEMS THAT YOU
   CHOSE TO BE INCLUDED WITH YOUR LOAN PAYMENT. 
THE EFFECTIVE DATE OF YOUR NEW SCHEDULED PAYMENT IS 00/00/00.'
        };

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)