Unable to insert form data into wordpress database in Vantage premium theme

Hi,

I have created a tabbed customize-page. In that, I have multiple forms on single page in different tabs. I am trying to insert data into wordpress database where I have created table “wp_form_user”. But nothing is being inserted. I request to please help me. I am not getting any error.
I have all these files in vantage-child theme folder.

custom_page.php

</div>
    	<!-- added content ends -->
        <div id = "sidebar1" class="sidebar">
            Please answer the following Questions


			<form action="http://ifast.uic.edu/index.php/successpage/" method ="post" name="tab1_form">
			  1. What are the key mathematical concepts?<br>
			  <textarea rows="2" cols="30" id = "tab1_ans1" name="tab1_ans1"></textarea>
			  <br><br>
			  2. How might students solve the problem? (2+ ways)<br>
			  <textarea rows="2" cols="30" id = "tab1_ans2" name="tab1_ans2" ></textarea>
			  <br><br>
              3. How do we reduce time spent on this part of the task?<br>
              <textarea rows="2" cols="30" id = "tab1_ans3" name="tab1_ans3" ></textarea>
              <br><br>
              4. What important misconceptions may arise?<br>
              <textarea rows="2" cols="30" id = "tab1_ans4" name="tab1_ans4"></textarea>
              <br><br>
			  <input type="submit" value="submit" name="submit">
			</form> 

        </div>

action_page.php

<?php
/**
 * Template Name:Php success page
 * The template for displaying all pages.
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site will use a
 * different template.
 *
 * @package vantage
 * @since vantage 1.0
 * @license GPL 2.0
 */

    require( dirname(__FILE__) . '/wp-config.php' );
    require( dirname(__FILE__) . '/wp-load.php' );


    
            //if (!empty($_POST)) {
            global $wpdb;
            echo 'here';
            $wpdb->insert( 'wp_form_user', array(
                'q1_value'    => 'q',
                'q2_value'    => 'd',
                'q3_value'    => 'd',
                'q4_value'    => 'f',
                'q5_value'    => 's') ,
                array('%s','%s','%s','%s','%s'));
            // if($success){
            // echo 'data has been save' ; 
            // }
//}
 ?>
<!-- script to insert data starts here-->

when I am getting echo post content, But I am not able to insert content. So tried to hardcode the values but still nothing is being inserted. I tried to replace with

require_once(‘../../../wp-config’) but its not working. So almost all the solutions given online, i tried. I have changed format an removed the format option. So its not working. I would appreciate any help. As I am new to wordpress, I can’t imagine anything.