Users need to be careful in case they're not willing to continue and purchase Prime services after the trial period ends as Amazon does not take permission or notifies before charging for the Prime services. just take care that after raising the request for canceling Prime, you also turn off the auto-renewal option of the payments. This way, you'll never again be charged with being notified. it's thus suggested that the users keep a track and cancel the Prime membership themselves before the thirty-day trial period ends. this way they are not charged any money.

If I cancel Amazon Prime, do I get a refund?
But you are accidentally or unwillingly charged for Prime, you'll get a refund if you instantly ask for it. If your card has been charged with the Prime membership after the free trial and you have got not used any of the Prime services after the paid subscription, you are then eligible to get a full refund of the amount you were charged for Prime. you'll not be charged any money for Amazon Prime, neither for the free trial nor for the payments for Prime post that. you just need to visit Amazon help page and cancel your Prime subscription and ask for a refund. Although, if no Prime services are used, Amazon automatically refunds back the full amount.
https://amazonprimerefundinfo.com