Apple Support Unable to Restore Confirmed Book Purchase - How to Escalate Issue?

A book I purchased 2.5 years ago suddenly disappeared from Books, and after 2 hours on the phone with 5 different Apple Support agents they are finally saying that notwithstanding they see the original purchase order, that they cannot restore it as it no longer exists. Technically it does exist, but the book has been divided into 2 parts for some reason (was recently made into a TV series) and its now significantly more expensive. Wouldn’t even offer me a credit for original purchase. I was finally told by the last “senior agent” that it is out of her hands, that she escalated the issue and I may or may not get a response from senior management in 3-5 days if they deem it appropriate.

This is obviously disappointing behaviour and makes me second guess whether I should be buying any more movies or books from Apple if they can just disappear and they can tell me sorry, its not our problem even when I supply them with the order confirmation.