An IRS letter 5071C is for verifying your identity - https://www.irs.gov/individuals/understanding-your-letter-5071c-or-6331c

What did you receive that told you your tax return was changed so that now you owe?

Look at that billing notice carefully ...which tax year are they referring to ?  What are the numbers after the CP or LTR  in the upper right hand corner ?  

If your 2020 return has a stop on it for ID verification then is cannot be for that one yet. 

Hello, I filed with TurboTax, and was told I would receive a refund of $1200.00: I then received a 

letter from the I.R.S saying I owe $4000.00, and I don't know how I should move forward with this!

its for year 2020

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@cornellelem1 wrote:

Hello, I filed with TurboTax, and was told I would receive a refund of $1200.00: I then received a 

letter from the I.R.S saying I owe $4000.00, and I don't know how I should move forward with this!

 

 

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As previously stated, what is the letter or notice number from the IRS, usually preceded by either a CP or LTR in the upper right of the first page.?

The letter or notice should tell you exactly what and why the IRS changed your original tax return so that you now have taxes owed.  It should also have a phone number for you to call if you have further questions or a response form to indicate you either agree or disagree with the IRS letter or notice. 

That is a $6,200 difference.  Does you return show any 6200 amount?  Like for withholding or estimated payments or extension payment?

A common reason this year is having the wrong amount on 1040 line 30 for the Recovery rebate credit.  Do you have an amount on line 30?  How much?