PHP pdo query insert twice sometime - php

Question

I have a android app which submit data through php but sometime the data insert twice when I submit the data.
I'm sure the issue is not on the app as the button is disabled once I press the button. Please help me spot my mistake. Thanks!
Following is the data inserted:
Following is my query:
if ($_SERVER['REQUEST_METHOD'] == 'POST'){
$area = $_POST['area'];
$date = $_POST['date'];
$batch = $_POST['batch'];
$workerName = $_POST['workerName'];
$remarks = $_POST['remarks'];
$time = $_POST['time'];
$tank = $_POST['tank'];
$sid= '';
$submissionDateTime = $_POST['submissionDateTime'];
require_once 'connectdb.php';
$stmt = $conn ->prepare("SELECT DISTINCT sid FROM feedingforms WHERE area = :area AND tank = :tank AND date = :date AND batch = :batch AND time = :time");
$stmt->bindParam(":area", $_POST['area']);
$stmt->bindParam(":tank", $_POST['tank']);
$stmt->bindParam(":date", $_POST['date']);
$stmt->bindParam(":batch", $_POST['batch']);
$stmt->bindParam(":time", $_POST['time']);
$stmt->execute();
$stmt->fetch();//fecth
switch ($stmt->rowCount() > 0){
case "0":
$stmt2 = $conn->prepare("INSERT INTO feedingforms(sid, area, date, batch, workerName, submissionDateTime, remarks, time, tank) VALUES(:sid, :area, :date,:batch,:workerName,:submissionDateTime, :remarks, :time,:tank)");
$stmt2->bindValue(":sid", $sid);
$stmt2->bindValue(":area", $area);
$stmt2->bindValue(":date", $date);
$stmt2->bindValue(":batch", $batch);
$stmt2->bindValue(":workerName", $workerName);
$stmt2->bindValue(":submissionDateTime", $submissionDateTime);
$stmt2->bindValue(":remarks", $remarks);
$stmt2->bindValue(":time", $time);
$stmt2->bindValue(":tank", $tank);
if ($stmt2->execute()) {
$result["success"]= "1";
$result["message"] = "success";
echo json_encode($result);
$conn = null;
exit;
break;
}else{
$result["success"]= "0";
$result["message"] = "error";
echo json_encode($result);
$conn = null;
exit;
break;
}
default:
$result["success"]= "2";
$result["message"] = "duplicate";
echo json_encode($result);
exit;
$conn = null;
}
}
?>