turbo tax softwear error. IRS sent me a letter stating i now owe money plus intrest.

The IRS sent letter 6475 to EACH spouse who received a 3rd EIP payment.   So if you filed a joint return and have one dependent then EACH of you should have a letter that shows $2100.   (3 x $1400 = $4200     and $4200 divided by two = $2100 per spouse)

If you answered incorrectly for the total amount you received for that 3rd stimulus payment, that is why your refund was reduced.

LOTS of people have made mistakes this year with the recovery rebate credit by "forgetting" that they received the $1400 per person stimulus checks last year.  They answered no to the questions for the  recovery recovery rebate credit and put the $1400 per person on line 30 of their returns.  But you cannot get it twice, so the IRS removes it when it is there by mistake.

Try checking your online account with the IRS

https://www.irs.gov/payments/your-online-account

Does the IRS show that you received a $1400  per person stimulus or EIP check in 2021?   Did you receive it?   When you were asked on your tax return did you say no?   Was there $1400 on line 30 of your tax return?

If the IRS says you got $1400 per person last year but you did not receive it you can have it traced.

LOST THIRD STIMULUS CHECK

https://www.irs.gov/newsroom/questions-and-answers-about-the-third-round-economic-impact-payment-topic-j-payment-issued-but-lost-stolen-destroyed-or-not-received

If you need to trace a payment that the IRS says has been issued to you, mail or fax a completed IRS Form 3911, Taxpayer Statement Regarding Refund.