调用未定义的方法codeigniter异常

I am to totally new to codeigniter and php if someone help with my code regarding this error I will really appreciate . error An uncaught Exception was encountered Type: Error

Message: Call to undefined method Mod_main::getSteam()

Model - Mod_main.php

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Mod_main extends CI_Model {

    public function getSteam()
    {
        $query = $this->db->get("tbl_stream");
        if($query->num_rows() > 0){
            return $query->result();
        }
    }

    public function getDistrict()
    {
        $query = $this->db->get("tbl_district");
        if($query->num_rows() > 0){
            return $query->result();
        }
    }

}

Controller - Con_main.php

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Con_main extends CI_Controller {  

    public function index()
    {

        $this->load->model('mod_main');
        $getSteam= $this->mod_main->getSteam(); 
        $getDistrict = $this->mod_main->getDistrict();  
        print_r($getSteam); 
        print_r($getDistrict);  
        exit();     
        $this->load->view('main',['getSteam'=>$getSteam, 'getDistrict'=>$getDistrict]);
    }
    public function getZ()
    {
        echo "hello" ;
    }
}

Classes are case sensitive. Use :

$this->load->model('Mod_main');
$getSteam= $this->Mod_main->getSteam();