Contact R&R.  They can fix it in the system for you.

You can just wait. If you send to an inactive member, then your book will automatically be marked received on the system action date on your screen.

It won't go lost in the system if the account is no longer active, it will automatically be marked as received. In the books you mailed tab, there is a date followed by "do not contact us before this date", try to honor that if at all possible. They do not have to time to get involved in every transaction and would like us to wait to see if the transaction will be completed without interference. A book shipped on the 10th could easily get marked as received yet. If you cannot wait for the credit, its possible they can clear the transaction sooner, if you can wait, try to let the system do its thing.

It's not a mark against you if their account is no longer active. And really it's only a mark against you w/active accounts if it happens quite a bit. 

ditto to wait until day 26 because you WILL receive your credit automatically.  This happened to me last year and while I don't always have a lot of patience I wanted for the system to do its thing.

most likely if you contact R&R they will not do anything because the system is set up to give you your credit automatically on day 26 since the member is no longer active