Dark pattern + invisible subscription = profit
So we did have weird AMZN... charges on our credit card, which didn't show up in the account on the Amazon website.
I called them just to check if it was really them, and the the guy immediately says yeah, I see those charges, they're for your Kindle subscription. What Kindle subscription?
1) Turns out that when you install the Kindle app on your phone, you get one of those magical dark patterns, which looks like this: screenshot
If you hit the big yellow button in the middle, you need to remember to cancel within the week, otherwise the free pass is renewed into a paying monthly subscription. I guess the back button is the only way to refuse the offer.
2) Their customer support could see our Kindle subscription, and the charges. However, we could not. Neither were showing in our account. Seeing the charges on the credit card was literally the only way we could notice anything was wrong...