面对使用ajax填充状态的问题

I am trying to populate the error to the user using ajax, values are saving in a database properly in every query but when trying to show the same in the front end it is not reflecting the same to the end-user.I wanted to populate the status to the end-user using ajax.

Here is my AJAX code

$.ajax({ 
url:"controller/client-registration-Controller.php",
                   type:'POST',
  contentType:false,            
  data:data,
   dataType : 'json',
   cache: false,
  processData:false,
     beforeSend: function(){
                $('#insert').attr("disabled","disabled");
                $('#fupForm').css("opacity",".5");
            }, 
            success: function(strMessage) {

                   $responseText=JSON.parse(strMessage);
                    if($responseText.status=='OK')
             {
              toastr.success(' Registered Successfully.', 'Success Alert', {timeOut: 5000});

                //clear all fields
                $('#fupForm').trigger("reset");
             }

                   else if($responseText.status=='ERR'){


                      toastr.error('You Got Error', 'Something  Went Wrong!', {timeOut: 5000}); 


                   } 
                   }


        });

}
        });

 });

  </script>

Here is my PHP Code

if (mysqli_num_rows($query) > 0) {
    header('Content-Type: application/json; charset=UTF-8');
    $response['status'] = 'ERR';
    $response['message'] = "Mobile is already exist";

    return json_encode($response);
    $res = " Mobile is already exist";

    echo json_encode($res);
} elseif (mysqli_num_rows($query1) > 0) {
    header('Content-Type: application/json; charset=UTF-8');
    $response['status'] = 'ERR';
    $response['message'] = "Email  is already exist";

    return json_encode($response);

    $res = "Email  is already exist";

    echo json_encode($res);
} elseif (!mysqli_query($con, $sql)) {
    $response['status'] = 'ERR';
    $response['message'] = "Something Went Wrong";

    return json_encode($response);
    $res = "Something went wrong";

    echo json_encode($res);
} else {
    header('Content-Type: application/json; charset=UTF-8');
    $response['status'] = 'OK';
    $response['message'] = 'Inserted successfully';

    echo json_encode($response);
    return;
    //  $error="Registered Successfully";
    // echo json_encode($error);
}

}
}}

I want to populate the status in the front end