I have changed the code and this is how it looks now-

#!/usr/bin/perl -w

use MIME::Lite;
use strict;
use warnings;

my $mail_host = 'servername.com';
my $to='fname.lname@sun.com';
my $from="west";
my $subject="Reports";
my $body = "See attached reports.\n";


### Create the multipart container
my $msg = MIME::Lite->new (
  From => $from,
  To => $to,
  Subject => $subject,
  Type =>'multipart/mixed'
) or die "Error creating multipart container: $!\n";

### Add the text message part
$msg->attach (
  Type => 'TEXT',
  Data => $body
) or die "Error adding the text message part: $!\n";

### Add the file
$msg->attach (
   Type => 'text/plain; charset=UTF-8',
   Path     => '/dir/dir/dir/report',
   Filename => 'test.txt',
   Disposition => 'attachment'
) or die "Error adding untouched_tickets.csv: $!\n";

### Send the Message
MIME::Lite->send('smtp', $mail_host, Timeout=>60);
$msg->send;
[download]

Content of the test.txt on server is -

this is a test message

However content of the test.txt which came through email is -

mkStats.pl
CheckDB.pl
CleanUp.pl
reports.pl
[download]

So the attachment is containing these 4 file names everytime I send email, no matter which file I am attaching.