Unable to insert data into using custom plugin

I am trying to insert some data in database which will be received from a form but the array of $wpdb is blank. There is no error reported by WordPress still the records are not been inserted. This page is not in admin panel. I am adding this code in a page called holiday-list through creating a short code while the plugin is been activated.

Below is the code.

<?php 
function form_creation(){
global $table_prefix, $wpdb;
$table_name = $table_prefix . "holiday";
$state_table= $table_prefix . "state";
?>
  <div>

  <h2>Holiday List</h2>
  <?php
 if($_SERVER["REQUEST_METHOD"] == "POST" && isset($_POST["submit"])){
  ?>
  <h2>Add Holiday</h2>
  <form name="add-form" action="<?php echo get_home_url(); ?>/holiday-list" method="POST">
      <input type="text" name="holiday_name" placeholder="Name of the Holiday" required>
      <input type="date" name="date" placeholder="select date" required>
      <select name="state_form_select" required>
          <option value="none">None</option>
          <?php
          $results = $wpdb->get_results( "SELECT id,state_name FROM $state_table ORDER BY state_name ASC"); // Query to fetch data from database table and storing in $results


    foreach($results as $row){   
        ?>
          <option value="<?php echo $row->id; ?>"><?php echo $row->state_name; ?></option>;
        <?php
    }

          ?>

      </select>
      <input type="submit" name="state_submit">
  </form>

  <?php
  }
   else if($_SERVER["REQUEST_METHOD"] == "POST" && isset($_POST["state_submit"])){

      $holiday_name = $_POST['holiday_name'];
      $date = $_POST['date'];
      $state_form_select = $_POST['state_form_select'];

      $wpdb->insert( 
    $table_name, 
    array( 
        'holiday_name' => $holiday_name, 
        'date' => $date, 
        'state' => $state_form_select, 
    ) 
);
      $success = $wpdb->insert($table_name, array(
   "holiday_name" => $holiday_name,
   "date" => $date,
   "state" => $state_form_select,
));

 if($success) {
     echo $success;
 echo ' Inserted successfully';
      } else {

   echo 'not';
   }
}



  else{
    echo $table_name;
  ?>
  <form name="add-button" action="http://connect.narayanbhargavagroup.loc/holiday-list/" method="POST">
      <input type="submit" name="submit" value="Add Holiday">
      </form>
  <table width="100%" border="1" cellpadding="5" cellspacing="0">
      <thead>
          <tr>
      <td>Sr.No</td>
      <td>Holiday</td>
      <td>Date</td>
      <td>Day</td>
      <td>State</td>
          </tr>
      </thead>
      <tbody>
          <tr>
          <?php
$results = $wpdb->get_results( "SELECT * FROM $table_name"); // Query to fetch data from database table and storing in $results


    foreach($results as $row){   
        ?>
        <td><?php echo $row->id; ?></td>
        <td><?php echo $row->holiday_name;?> </td>
        <td><?php echo $row->date; ?></td>
        <td><?php echo $row->day; ?></td>
        <td><?php echo $row->states; ?></td>
        <?php
    }
?>
          </tr>
      </tbody>

      </thead>
  </table>
  </div>

<?php
  }
}
add_shortcode('test', 'form_creation');

Below is the create table syntax i am using code so for table structure understanding.

CREATE TABLE `connect_holiday` (
  `id` int(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
  `holiday_name` varchar(250) NOT NULL,
  `date` varchar(128) NOT NULL,
  `day` varchar(50) NOT NULL,
  `states` varchar(250) NOT NULL,
  `addedby` varchar(250) NOT NULL,
  `added_on` varchar(250) NOT NULL,
  `last_edited_by` varchar(250) NOT NULL,
  `timestamp` varchar(250) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;