Plugin isn’t handling orders properly

in class-wc-commerce-helcim.php line 470-475 you have the following code:

public function process_payment( $order_id ) {

		global $woocommerce;

		// GET ORDER
		$order = new WC_Order( $order_id );

This is incorrect way of getting orders, it is causing duplication of the orders.

Please change last line of your code to

$order = wc_get_order( $order_id );

Thanks!