Refund for an item that has been delivered

Do Amazon ever refund refunds ? Just before Christmas I had an oder for a book, which I duly posted off. A month later I got a request for a refund as it had not arrived. I was pretty suspicious, but knowing Amazon always sides with the customer, I paid up.
Today, doing a quick review of my ‘voice of the customer’ feedback, i find a review of ‘excellent’ against the item. So its pretty obvious that she received it, and on time and in the advertised condition. No possible basis for a claim. So do I complain to Amazon ? will I get anywhere.? I have already messaged her to say i will be starting a complaint ( she can sweat for a bit if nothing else ).
Ok, I could have checked before refunding, but it honestly never occurred to me that anyone would try anything that blatent. And, going forward, what would happen if I refused to pay up in a similar case ?