Valid question. I was switching bank accounts at that time, so it's possible the card was not expired but linked to an account that did not exist anymore. Might also have been the account itself and not the card that was listed (Lastschriftverfahren, where they take money directly from the account). I'm fuzzy about the details, not really because it was particularly long ago (~2 years), but because it was confusing back then.

Edit: Had a look at my writeup in my blog [0], Lastschrift it was. Amazon picked a bank account that did not exist anymore to pay for the order. When that bounced came the fees - and while one fee for that would have been normal if I had given the wrong bank account (which I'm pretty sure I only did, if I did, because their system did not save when I changed the bank account before), to take multiple fees for one order was in no way okay.

[0]: https://www.onli-blogging.de/1832/Meine-richtig-schlechte-Su... (in german)

This has happened to me. In some circumstances banks will still honour a charge even though the card is expired.

You'll have to ask the banks why. In my case it wasn't a problem, but technically it shouldn't happen and it's strange that it did.

That actually could have been a problem. If the bank had accepted the charge, the fee for that would have been high, as far as I read when closing the account. This way - by Amazon just getting a bounce - my annoyment was just about the unreasonableness of the fee (to pay 3x3€ instead of 1x3€ just because Amazon decided to split the order), if the bank would have charged me instead it could have become a money problem.

That added to my concern with Amazon just using the wrong bank account, and that old account occuring again and again in my profile. Even if I wanted to order something at Amazon it would be too risky now.

Amazon doesn't charge your card until it's about to ship your order. Thus an order with an invalid card will go through but won't ship.