Thank you for your question.
If you only received one confirmation e-mail, it means the ticket was sold only one time.
Therefore you were not charged two times. The first try with Twint did not go though definitively.
TWINT authorizations are not definitive charges, although they are displayed on the bank account. The money is "reserved" as an authorization, and if there is no ticket sold, it is automatically released again. This can take between 7 and 14 days with TWINT. Once the amount has been released, it will no longer be visible on your bank statement. For this reason, we recommend that you always wait for the final bank statement.
Please contact your bank for further information on the means of payment.
Tip: We recommend purchasing tickets with SwissPass-login. So your orders are visible in your account. Please log in on sbb.ch/en and click on "Orders". If the booking is not listed, it did not work and your means of payment was not debited.
If you do not yet have an SwissPass account, you can create one using the following link: sbb.ch/en/reg
I wish you a nice day!