I think you have to remove your payment data so they will not Auto charge you. Your acct will go to FTP when your paid time is up.
I just went to check. They JUST changed something on the Membership screen. It used to include a cancel button up to a few days ago. Screen is different now and is no longer showing the cancel button. It also used to show the subscription plan you were on but now it shows the information differently. Anyway something has changed in the last couple of days.
There was an issue preventing it from appearing. This issue has been resolved and the button should appear.