CodeIgniter model method which collects submission data fails to insert record without editing an error

I was trying to insert data in database, but it's not working properly. There's no data inserted data in database and no error. I activated the helper and auto-load is written.

my controller

public function save()
{
    if ($this->input->post('submit')) {
        $this->Checkout_model->process();                
    }
}

my model

function process()
{
    $name = $this->input->post('name');
    $phone = $this->input->post('phone');
    $email = $this->input->post('email');
    $address = $this->input->post('address');
    $data = array(
        'name' => $name,
        'phone' => $phone,
        'email' => $email,
        'address' => $address               
    );
    $this->db->insert('customers', $data);
}

Use this code In Controller

public function save() {
    if($this->input->post('submit')) {
    $name = $this->input->post('name');
    $phone = $this->input->post('phone');
    $email = $this->input->post('email');
    $address = $this->input->post('address');
    $data=array (
        'name' => $name,
        'phone' => $phone,
        'email' => $email,
        'address' => $address               
    );
        $this->Checkout_model->process($data);                
    }
}

In Model

function process($data) { 
    $this->db->insert('customers',$data);
}