The iTunes Store has no record of past Audiobook purchases
I would advise you to take your question directly to the iTunes Store personnel, they are the ones who keep track of user accounts and purchases made.

You will want to be able to provide them the billing address and payment method you used for those purchases. Also, if you can find any of the invoices that Apple emails between a few hours to a few days after each purchase - you can also let the Apple Store support person you contact that email in case your Apple ID is different than the email on file.