If I received a refund on my 2018 taxes why am I receiving a notice that I now owe?

[Critter-3]

The IRS reviews returns up to 5 years later ... so did you get a CP 2000 notice ?   If so review the notice carefully ... what did they say you missed?  

[xmasbaby0]

TurboTax does not receive any information from the IRS  (or state) after you file your tax return, so no one at TT knows about a notice you got from the IRS or why they sent it.  

What do the letters from the IRS mean?

https://ttlc.intuit.com/community/irs/help/i-got-a-letter-or-notice-from-the-irs/00/27100

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

If you did not purchase Audit Defense:

TurboTax has a special phone number for help with IRS 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/