TurboTax guarantees that the CALCULATIONS will be accurate. TurboTax is a self-prepared tax return. TurboTax cannot guarantee that you enter everything accurately and completely, or that you enter everything in the right place. Many errors are user errors, for which TT is not responsible. So what error occurred with your return?
After preparing my return and getting a refund amount expected, the IRS amended the refund and over doubled my return (I got back more than TurboTax calculated). My concern is that now I question the validity of TurboTax calculations and that I should be getting more back than TT indicates in future returns. All the IRS documentation said was that there was a miscalculation in my tax owed.
You would need to provide more information and have a better understanding of what exactly the IRS changed on your return. The IRS frequently uses the term "calculation error" generically when they change something.
And the "error" did not cost you anything.
You can contact customer support to discuss it.
To call TurboTax customer support
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number
They are available from 5 a.m. to 5 p.m. Pacific time Monday - Friday.