$stmt = $conn->mysqli->stmt_init();
$stmt = $conn->mysqli->prepare('SELECT Username, EmailVerified, Blocked FROM user WHERE Email = ? AND SLANumber = ? AND Password = ?');
$stmt->bind_param('ssb', $_POST['EmailID'], $_POST['SLANumber'], $_POST['Password']);
$stmt->execute();
$stmt->store_result();
$result = $stmt->get_result();
if($result->num_rows == 0){
    echo 'No rows found';
}
else{
    // Continue processing here
    .....
}

$stmt->execute();
// $stmt->store_result();
$result = $stmt->get_result();
if(result->num_rows == 0){
  ...
}

$stmt->execute();
// $stmt->store_result();
$result = $stmt->get_result();
if($stmt->affected_rows == 0){
  ...
}

$result = $stmt->get_result();

// Also check strict comparison against int 0,
// to avoid incorrect equality with boolean FALSE
if($result->num_rows === 0){
    echo 'No rows found';
}