The charges are coming from pre-existing ride credits that were applied before you requested to cancel your account; they're separate from "actual" money you've put into the system through payment methods like credit cards or Paypal. But don't worry - when you delete your account, all ride credits are converted to cash and put in your Uber user account's wallet. You'll be able to access that cash by going into the "Payment" tab in your app, scrolling down below "Add Payment Method," and tapping on either "Account Balance" or "Promo/Referral Code." (source)