Found out yesterday that we are members of amazon prime - I certainly did not join this; and can only think that OH did so inadvertently - there is an order from him for some light bulbs on the same date as the membership started. They have had £79 from us!! - I am jolly cross, and have of course cancelled it, but we will remain members till November.
I looked into it and note that all their orders result in an email; but the prime membership does not - there is a confirmation hidden away in your account details which I had to search for.
I know that we are not alone in this happening inadvertently - there is a veritable plague of fellow victims on the net - but there seems to be no redress for this, and they are allowed to continue this underhand practice.
Looking at the site I can see how you might click the wrong thing, especially if, like my OH, you seldom use the net.