Woocommerce Order Completed Email with prepaid value using Germanized plugin

Question

I am using Woocommerce with the Germanized Pro Plugin. After successfull payment my customer gets the email "order completed". The regular mail from woocommerce with the order details. The customer was buying prepaid value for a customer card. Therefore I would like to tell him the new value he has available for his next purchase at my local store.

I placed the follwing code to my functions.php in my child theme. But it is just doing nothing. As first step I just want the text: "Your new prepaid value" to be shown. Anyone has an idea why?

add_action( 'woocommerce_email_before_order_table', 'add_prepaid_value_to_mail', 10, 4 );

function add_prepaid_value_to_mail( $order, $sent_to_admin, $plain_text, $email ) {
    echo '<p>Your new prepaid value:</p>' ;
}