I've never received an itemized receipt but I keep track of my refunds with the information I get from the Order Status page. I click on "View My Order" to see the price of the item, the cost of s&h, and the amount charged for tax. If paid on easy pay, the # of easy pays are shown--whether it was 3, 4, 5, etc.
Once I return an item I look at my CC statement online to see how many easy payments were made. If, for example, there were already 2 paid, I add those together to get the total $ amount I've already paid. I then deduct s&h and return postage from that total. If I paid return postage myself, of course I wouldn't deduct the amount for the return postage. The refund amount is listed right under the item so it's easy to check that it matches my total.
eta - if you don't want to check your bank statement (which I would never advise), but if you just want a quick check of how many of the easy pays you already made on an item, you can simply click on "Easy Pays" to see how many were already paid. If you see you're on 3 of 4 for the upcoming month then you know that the first 2 were already paid.