So it might have been "free" for a month, I don't know what exactly you signed up for. This is something you should have read beforehand. You most probably approved this payment when you signed up and it was on you to be careful about what you approve. Now all you can do it cancel the payment so you don't get the deduction next month too.
It's not a free lesson, but hopefully it's a memorable one that would protect you from suffering from the same thing with larger sums. I personally made a cock-up like that with a larger sum, so I know exactly how you feel, but all you can do is learn your lesson and be more careful what you sign up for with a payment method in the future.
But you can rest assured that Amazon were not technically scamming you and there is probably no way to get the money back.