php - Call to undefined method on calling DB Class -

i've been struggling little while code should take care of (is not mine 1 of biggest issues). original programmer unresponsive , unwilling help; improve situation further.

the code page content shown, e-catalog. flow of items @ bottom consists of 10 items, fatal error on calling php database information:

fatal error: call undefined method db::connection() in c:\xampp\htdocs\menonitapp2\api\modelos\productos.php on line 128

the error occurs here:

require_once "db.php"; //the db info file. require_once "producto.php"; require_once "subasta.php"; class productos {  private function __construct() {   //actually empty constructor.  } //other functions  public static function buscar_primeros($id, $bus, $counting){    $min = $counting;    $max = 10;    $statement = db::connection()->stmt_init(); //where error occurs    //more stuff after  } } 

and full db.php file access database:

class db {   private static $servername = "localhost";   private static $username = "root";   private static $password = "********";   private static $dbname = "taquionm_menonitapp";    private static $connexion = null;    static function connection() {     if(is_null(self::$connexion)) {        self::$connexion = new mysqli(self::$server, self::$username, self::$password, self::$dbname);       self::$connexion->set_charset("utf8");       if (mysqli_connect_errno()) {         printf("connect failed: %s\n", mysqli_connect_error());         exit();       }     }      return self::$connexion;   } } 

other relevant information: using xampp 5.6.8 on windows 8.1. php version 5.6.8 well.