Inertia
I feel like I could... TAKE ON THE WORLD!!
I did similar and only realized after the cut off what had happened, I contacted them and they cancelled and refunded my money straight away.I think the trap people most often fall into on Amazon is to click the trial free delivery option at checkout. Once you've done that you've signed up for an Amazon Prime account and the subscription is taken from your bank account once the trial period is over unless you cancel it. A lot of people don't realise that they're signing up and so it doesn't occur to them that they have anything to cancel.
Unless you're someone who meticulously checks their bank account this reoccurring payment will just keep being collected annually without you ever knowing
Amazons customer service is extremely good, they are playing the long game, its no good to them to scam you and then lose you as a customer. They want all your business.