How do I get a refund of $99.00 for prime membership that I have no idea why I was charged for this.

About the Amazon Prime Membership Charge At the end of the Amazon Prime free trial or annual membership period, your card will be charged $99 automatically for the next membership period.
The annual charge for Amazon Prime includes FREE Two-Day Shipping, Prime Instant Video, and the Kindle Owner's Lending Library.
If you didn't intend to convert your membership to a full 12-month membership, you can cancel your Amazon Prime membership on the Manage Prime Membership page. If you haven't placed an Amazon Prime-eligible order, you are eligible for a full refund.
When we renew your membership, the card you gave us at sign-up is used. If we can't successfully charge this card, another payment method will be used. Your initial sign-up authorizes us to use the preferred or other available payment methods. To update your preferred card, go to Manage Prime Membership .