What do I do if I mailed my tax return and Turbotax says I never filed.

TurboTax has no way to know that you put your tax return in an envelope and took it to a mailbox.  The tax software did not see you do that.  The software only knows that you did not e-file or at least that you did not e-file successfully.

MAILED RETURNS

The IRS has just started to work through millions of mailed returns that have been piling up in trailers during the pandemic.  All you can do is watch the IRS refund site to see when your return makes it to the surface and goes into processing. Sorry.

Per the IRS website IRS Operations During COVID-19: Mission-critical functions continue:

IRS operational status and alternatives

Processing Delays for Paper Tax Returns: Taxpayers should file electronically through their tax preparer, tax software provider, or IRS Free File. 

We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.

Do not file a second tax return or contact the IRS about the status of your return.

If  you mail a tax return (or a payment) to the IRS, it is a good idea to use a mailing service that will track it like UPS or certified mail so you will know it was received.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. 

TurboTax will not know anything about your mailed return, and will continue to show “Ready to Mail” on your account.  TurboTax will not know that you put your tax return in an envelope and took it to a mailbox.  TurboTax does not get updates on mailed  (or e-filed) returns.

When the IRS finally opens its mail and begins to process mailed returns you can check the status on the IRS site. https://www.irs.gov/refunds

State returns have to be mailed to the state.

https://ttlc.intuit.com/questions/1899433-how-do-i-track-my-state-refund