You would NOT have been charged $300+ for using the TurboTax Free online edition. That type of charge would only have been if you used one of the Live Full Service editions where a CPA would complete your tax return for you. Additionally, you were shown the amount of the charges in the File section of the program on Step 1 and you agreed to the charges.
Also, your message on this forum indicates you are using the TurboTax Free online edition.
See this TurboTax support FAQ for checking your fees - https://ttlc.intuit.com/community/charges-and-fees/help/how-do-i-review-my-fees-in-turbotax-online/0...
So there is much more to this story.
Contact TurboTax support and speak with an agent.
Support is open from 5am to 5pm Pacific time, Monday thru Friday
Use this website to contact TurboTax support during business hours - https://support.turbotax.intuit.com/contact/
Or -
Support can also be reached by messaging them on these pages https://www.facebook.com/turbotax/ and https://twitter.com/TeamTurboTax
