Hosting Free - mysqli PDO bug for default php 7x

hi admin i found mysqli pdo bug for PHP 7, below example code
Can you fix it? and why after i changed the php version, a php version does not change why? do i have to upgrade hosting

1. <?php
2. error_reporting(E_ALL);
3. 
4. $host = 'sql110.ezyro.com';
5. $user = 'ezyro_20892691';
6. $pass = 'social102';
7. $name = 'ezyro_20892691_webmestudio';
8. 
9. $db = new mysqli($host, $user, $pass, $name);
10. if($db->connect_error) {
11.     die('tidak terkoneksi ke database');
12. }
13. 
14. if($_SERVER['REQUEST_METHOD'] == 'POST') 
15. {
16. 	//deklarasi
17. 	$email = $_POST['mailverify'];
18. 
19. 	if(filter_var($email, FILTER_VALIDATE_EMAIL)) {
20. 
21. 		//cek di database
22. 		$sql = $db->query(select * from subscriber where email = '$email' );
23. 
24. 		if($sql->num_rows == 1) 
25. 		{
26. 			$json = [
27. 				'error' => false,
28. 				'alert' => 'Email tersedia siap download',
29. 				'link_download' => 'http://google.com' //ganti dengan link download
30. 			];
31. 		}
32. 		else
33. 		{
34. 			$json = [
35. 				'error' => true,
36. 				'alert' => 'Maaf email tidak tersedia ',
37. 				'link_download' => null
38. 			];
39. 		}
40. 	}
41. 	else 
42. 	{
43. 		$json = [
44. 			'error' => true,
45. 			'alert' => 'Email tidak valid'
46. 		];
47. 	}
48. 
49. 	echo json_encode($json);
50.         exit;
51. }
52. ?></t>

Please point out the bug and explain.
You can change PHP Version from control panel easily, you do not need to upgrade for that.

> @Admin said:

Please point out the bug and explain.
You can change PHP Version from control panel easily, you do not need to upgrade for that.

Example implementation, when I click download, but logic does not work on $ sql-> num_rows == 1, and always leads to notification error, while in the database, the data matches the data in the input earlier.