CRITICAL Uncaught Error: Call to a member function

Question

global $woocommerce; if(!headers_sent()){

            $billingcity    =  WC()->customer->get_billing_city(); // this line

            if(empty($billingcity)){

                if(isset($_COOKIE['set_my_city'])){

                    //setcookie('set_my_city', $city, time()+62208000, '/', $_SERVER['HTTP_HOST']);

                }else{
                    WC()->customer->set_props(array('billing_city'=> 'Bangalore Rural'));

                    $billingcity    =  'Bangalore Rural';

                    setcookie('set_my_city','Bangalore Rural', time()+62208000, '/', $_SERVER['HTTP_HOST']);

$billingcity = WC()->customer->get_billing_city(); error in this line