You do have the option to deposit your refund on to an existing prepaid card. You would just need the routing and account number, which you can get by calling the prepaid card's customer service number. You may want to check the legitimacy of the email. If you feel it was sent in error, I would use the link provided below to reach out to TurboTax directly or reach out to the prepaid card's customer service:
TurboTax Contact Us