Confirm the cancellation
When to use: Use it when the order has not shipped and you can cancel it right away.
Response
Done, customer name -- I have cancelled order order number for item, and nothing further will be charged or shipped. You do not need to do anything else on your end.
refund note. If you were on the fence for any reason, I am happy to help, but there is no pressure -- the cancellation is already processed either way.
If they explain why
Thanks for telling me, that is genuinely useful. It will not change anything about your cancellation, which is already handled, but I will pass the feedback along so we can do better.
Why it works
It confirms the cancellation as a completed fact, removes any sense that they had to earn it, and offers help without pushing -- which leaves an easy exit that people remember warmly and come back to.