Amazon Prime Double charged membership -- refused to refund

My wife and I have one credit card account with Amazon/Chase. But Amazon has been charging us for two Amazon Prime memberships. I called them up and they agreed we should not have been charged twice each year going back to 2016. They refunded years 2022 thru 2024 but refused to refund the 6 years from 2016 thru 2021, claiming the records are "grayed out" on the computer screen, even though they admit we should have never been charged for those years. They know exactly how much a membership costs for each of those years but refuse to refund our money. I asked them: "What married couple living in the same household requests two Prime memberships?"