Turbotax guarantees accurate calculations. It does not guarantee the accuracy of your information -- Turbotax has no way of knowing that you might have left off income or claimed a dependent you weren't allowed to claim.
You can try filing a claim here, but the claim must be filed within 30 days of receiving the error notice. You might be overdue on the 2016 return.
If the IRS is holding your 2017 return for extra examination due to the past mistake, that is also out of Turbotax's control.
https://ttlc.intuit.com/replies/4202723
