Rear wheel bearing replacement under warranty $650?

Had loud noise from our 2018 forester on highway (86k miles) and brought it to dealer who diagnosed rear wheel bearings. $100 deductible on our extended warranty covers the replacement BUT apparently they need to also replace the backing plates at $150/each and 1hr labor so total would come to $650 because dealership service says the warranty doesn't cover the backing plates.

Do I have any options to not pay $650 for service that should be covered under warranty or get any kind of reimbursement--is this a dealership specific thing? Is there a number I should call to open a case with Subaru of America?

I saw the 2016 foresters have a TSB https://static.nhtsa.gov/odi/tsbs/2019/MC-10165552-0001.pdf that calls out part numbers for the hub AND backing plates so it seems odd that my 2018 which is the same platform is not going to cover them in any way.