I was the same as Hopkirk 12.48. I was furious and emailed Amazon and said I wanted my free trial cancelled immediately with added moans about how annoyed I was.They emailed back that this had been done and I had no further trouble.
When I posted about this on AB some while ago lots of people expressed surprise, but it had obviously just been added to the website as it has caught many of you out now. Frankly I hardly ever shop on Amazon now, much prefer EBay.
When I read about people having purchases being made on their account that they had not initiated, I emailed Amazon to have my card details removed, so I could just pay each time. Apparently this is not an option, but when I logged in again, I have had extra security put on my account in the form of a Captcha.