Hooking into the cancelled subscription hook.

cancel-subscription-hook.php

<?php
/*
Plugin Name: Cancelled Subscriptions Hook
Plugin URI: https://gist.github.com/BFTrick/8696222
Description: Hook into the WooCommerce Cancelled Subscriptions hook and print the data.
Version: 1.0.0
Author: Patrick Rauland
Author URI: http://www.patrickrauland.com 
*/

function my_cancelled_subscription( $user_id, $subscription_key ) {

	echo "user_id is: ";
	print_r( $user_id );
	echo "\r\n";
	echo "subscription_key is: ";
	print_r( $subscription_key );

	exit();

}
add_action( 'cancelled_subscription', 'my_cancelled_subscription', 10, 2 );

result.txt

user_id is: X subscription_key is: XXXXX_XXXXX

I use standard paypal, when customer cancel subscription from paypal account, this code is not working. :(.
Other hook work well: add_action('processed_subscription_payment', 'subPay', 10, 2);