You would have to use two separate User ID's to purchase the TurboTax online edition more than once. If you have not e-filed a tax return using TurboTax using either User ID, then your two purchases would not prevent you from e-filing.
Did you use the IRS non-filers website to register for the stimulus and are now trying to e-file a 2019 tax return? If so, then see this TurboTax support FAQ for how to proceed - https://ttlc.intuit.com/community/tax-topics/help/stimulus-how-to-file-your-return-after-getting-reject-r0000-902-01/01/1602609
You will need to contact TurboTax support for any type of billing issue that requires a refund for a purchased TurboTax online edition.
Support is open from 5am to 5pm Pacific time, Monday thru Friday
See this TurboTax support FAQ on how to contact Support - https://ttlc.intuit.com/questions/3401489
Or -
Use this website to contact TurboTax support during business hours - https://support.turbotax.intuit.com/contact/
Support can also be reached by messaging them on these pages https://www.facebook.com/turbotax/ and https://twitter.com/TeamTurboTax
Download codes are [product key removed] and [product key removed] at $79.99 each. I am using the G5SA download. Please refund the duplicate amount.
You can go here TurboTax CD/Download Refund Request Form to request a refund if still within 60 days of purchase.
Buying the program twice is not your issue ... if it says it is a duplicate filing then did you file one of those NonFiler returns to get the Stimulus check earlier this year ?