Backdoor Roth IRA with contributions for 2019 & 2020 made in 2020

I believe I don't owe any taxes. How can I handle this?

 

This is the situation:

Not-deductible (post-tax) contribution to traditional IRA, this is the breakdown of my contributions:

  • 01/06/2020 - 6K contribution to traditional IRA (this is for the year 2019)
  • 01/07/2020 - 6K contribution to traditional IRA (this is for the year 2020)

After the contributions, I have converted the full amount (12,000$) to a Roth-IRA. This is the breakdown of the conversions:

  • 01/07/2020 - 6K conversion to ROTH-IRA (this is for the year 2019)
  • 01/08/2020 - 6K conversion to ROTH-IRA (this is for the year 2020)

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I've followed the following instructions: https://ttlc.intuit.com/community/entering-importing/help/how-do-i-enter-a-backdoor-roth-ira-convers... but 6,000$ of the 12,000$ are considered mistakenly taxable. 

 

I've tried to contact two times a live expert without success. They were not able either to solve the issue or clarifying the situation because in their opinion the amount was taxable.