You haven’t been charged twice! When you book a trip, a “hold” is placed on the estimated fare in your account, but money is not actually taken out. This is to check that there is enough money on the card for the trip to go through, and to check that the card is legitimate! Once the trip happens, you will be charged the real amount that the trip costed, and the “hold” will disappear. Sometimes it takes a couple of days for the hold to reverse, but there is no “second fare” that has been taken.