There have also been cases where a customer violated Amazon's terms of service and lost access to all of their Kindle e-books. Amazon has all the power in this relationship. They can and do change the rules on us lowly peasants from time to time.
Note, there are indeed ways to download your books and import them into something like Calibre (and remove the DRM from the books). If you do some web searches (and/or search YouTube) you can probably figure it out.
Amazon is on my shit list and will not buy any products from them ever again. They are one of the worst monopolist mega corporations. They treat their employees like slaves, are anti-repair, anti-consumer.
I gifted an older Kindle to my sister, and the screen broke (out of warranty). I contacted Amazon about it, and they basically said they don't make replacement parts and don't service the kindles, they can only give me a small discount for buying a new one.
I looked up a guide on doing it myself, and even if I find a replacement screen, it's really difficult. The screen is glued with a strong adhesive. The entire device looks very cheaply built and deliberately made really difficult to repair.
I mean to be fair they are very cheap to purchase all things considered. That said I’ve still got my Kindle 3 I bought used on eBay and it’s still going strong after like 10 years I’ve owned it.