After you file

Did you call and use the Audit Defense that you paid for?   Audit Defense can help you, but they cannot prevent the IRS from auditing you or seizing your refund if you made a big mistake on your tax return and actually owe the IRS.   TurboTax provides do-it-yourself tax software----the software cannot/does not check outside sources for your income or other information.   If you leave out income, enter something incorrectly, etc. the software cannot know that.   It sounds like you made some sort of error that led you to expect a refund that the IRS says you do not get.   You do not tell us what additional information you had to send to the IRS.

I RECEIVED A LETTER FROM THE IRS/STATE

TurboTax does not receive any information from the IRS or your state after your return was filed, so no one at TurboTax knows about a letter you received from the IRS or the state.

(what the letters from the IRS mean)

I GOT A LETTER FROM THE IRS   

https://ttlc.intuit.com/questions/3605673-i-got-a-letter-or-notice-from-the-irs

I AM BEING AUDITED

If you purchased Audit Defense:

https://ttlc.intuit.com/questions/2924451-i-bought-max-or-audit-defense-and-now-i-m-being-audited

AUDIT SUPPORT

TurboTax has a special phone number for help with IRS/state tax letters, which will be easier than going through regular Customer Support.   At the page below, click on the blue button that says "Get Help from TurboTax Support".  Then it will ask you what tax year is your letter.  Then it will ask you what the letter concerns. Then it will show you the phone number during posted business hours.

https://support.turbotax.intuit.com/irs-notice/audit-support/