WordPress Ajax not working to insert, query and result data

On my site, through a form I send/register same information in database, do a SELECT/query and return it! Return the last table saved in database, just that user just entered on the form (along with some more information coming from the database).

How I want to display these values coming from databse in a modal bootstrap it’s necessary that the page doesn’t give the refresh. For this, I inserted the AJAX as follows:

$(document).ready(function(){
      $('#enviar').click(function(){
          $.ajax({
          //CAAL  AJAX IN WORDPRESS
          url: 'wp-admin/admin-ajax.php',
          type: 'POST',
          //INSERT, QUERY AND DISPLAYS TO USER
          data: 'action=prancha',
          error: function(){
              alert('ERRO!!!');
          },
          //IF OK, DISPLAYS TO USER IN DIV "RESULT"
          success: function(data){
              $('#result').html(data);
          }
      });
    });
 });

MY FUNCTIONS.PHP:

function prancha(){
  header('Content-Type: text/html; charset=utf-8');

  include "../../../wp-config.php";

      /* DECLARING THE VARIABLES  */
  $nome = "";
  $email = "";
  $estilo = "";
  $experiencia = "";
  $altura = "";
  $peso = "";

  // VALIDATION
  if(!empty($_POST)){
     $nome = $_POST['nome'];
     $email = $_POST['email'];
     $estilo = $_POST['estilo'];
     $experiencia = $_POST['experiencia'];
     $altura = $_POST['altura'];
     $peso = $_POST['peso'];

     cadastra_user($nome, $email, $estilo, $experiencia, $altura, $peso);
 }

  //INSERT IN DATABASE NAME, EMAIL, ESTILE, EXPERIENCE, HEIGHT AND WEIGHT
function cadastra_user($nome, $email, $estilo, $experiencia, $altura, $peso){
    global $wpdb;

    $table = 'user';

    $data = array(
      'nome' => $nome,
      'email' => $email,
      'estilo' => $estilo,
      'exp' => $experiencia,
      'altura' => $altura,
      'peso' => $peso,
    );

    $updated = $wpdb->insert( $table, $data );

    if ( ! $updated ) {
      $wpdb->print_error();
    }
}   

//CONECT WITH DATABASE TO DO THE SELECT
include "db.php";

  function BuscaAlgo($conexao){

  // QUERY + INNER JOIN IN DATABASE
 $query = "SELECT  USU.usuario,
                   USU.nome,
                   USU.exp,
                   USU.altura,
                   USU.peso,
                   PRAN.exp_ref,
                   PRAN.altura_ref,
                   PRAN.peso_ref,
                   PRAN.tipo_prancha,
                   PRAN.tamanho_prancha,
                   PRAN.meio_prancha,
                   PRAN.litragem_prancha
                    FROM DADOS_USUARIO AS USU
                         INNER JOIN PRANCHA AS PRAN
                             on USU.exp = PRAN.exp_ref
                              WHERE USU.altura = PRAN.altura_ref
                                AND USU.peso = PRAN.peso_ref
                                  ORDER BY USU.usuario DESC LIMIT 1";

  $resultado = mysqli_query($conexao,$query);

  $retorno = array();

  while($experiencia = mysqli_fetch_assoc($resultado)){
    $retorno[] = $experiencia;
  }

 return $resultado;
}

//DISPLAYS THE QUERY TO USER
$resultado = array();
$resultado = BuscaAlgo($conexao);

foreach($resultado as $valor){
    echo $valor["usuario"]; print(".  .  .  .");
    echo $valor["nome"]; print(".  .  .  .");
    echo $valor["exp"]; print(".  .  .  .");
    echo $valor["altura"]; print(".  .  .  .");
    echo $valor["peso"]; print(".  .  .  .");
    print("///////");
    echo $valor["tipo_prancha"]; print(".  .  .  .");
    echo $valor["tamanho_prancha"]; print(".  .  .  .");
    echo $valor["meio_prancha"]; print(".  .  .  .");
    echo $valor["litragem_prancha"];
}  

    die(); //END THE EXECUTION
}
//ADD THE AJAX HOOKS IN WORDPRESS
add_action('wp_ajax_prancha', 'prancha');
add_action('wp_ajax_nopriv_prancha', 'prancha');

The code is commenting, basically I did:

AJAX:

• In the field URL call the native WordPress admin-ajax.php.
• In the field DATA call the function that makes the registration, query and displays to the user.
• In the SUCCESS field, prints the value of data.

FUNCTIONS: I make the registration code in database, do the query and print with the echo.

The AJAX is returning me the error message.

How can I solve this?
What am I doing wrong?

Note1: When I insert the code that is in my ‘functions, the registration code, the query and theecho’ to displays in a direct way, in my footer.php, it works. Therefore, we can understand that the error is not even in the code of insert,query or displays.

NOTE 2: I want to display the return of database within a modal boostrap. At first I’m just displaying on the screen, to check that everything is OK. After that I will research on how to put these data into the modal, although not the main subject of the post, suggestions for how to do this are also welcome.