IRS tax letter requesting $319 penalty for 2019 taxes. paid in full $13,540 July 10. 2018
Your question is unclear. I think you mean that you paid your 2017 tax bill on July 10, 2018, and the amount you paid was $13,540.
If that is true, then you owed a substantial penalty for 2017 both for being late and for under-paying throughout 2017 to end up that far behind. In that case, Turbotax might have offered to calculate the penalty for you, but it is only an estimate, because only the IRS calculation of penalties is deemed correct. If the IRS is now asking for an additional penalty and interest amount because the amount calculated by Turbotax in July, 2018, was not high enough, that situation is not covered by the accuracy guarantee.
