Answers on an email.
When two boxes arrived on Monday afternoon (one with the first order, without the cancelled items, and the other with the second order) Christopher returned the items from the first order, inclulding the cancelled items, and applied for a reimbursement of the shipping costs. Amazon's email engine did cater for "returns and refunds" but only for items which were on an order. If an item didn't appear on an order (e.g. if the item was dispatched despite being cancelled and arrived despite no longer appeared on an order) then there was no option to send the email. Christopher had to misinform Amazon about the reason for the email in order to send it.