If you used Online TurboTax for your 2018 return, log in and go to the section "Your Tax Returns & Documents". Expand that section and choose tax year 2018. What term is used to describe the status of the 2018 return--does it say accepted, rejected, printed, started, or what?
If it was successfully efiled, it should say "accepted". In that case you'll need to speak to the IRS about any 2018 refund you didn't receive so they can troubleshoot with you. Unfortunately, the IRS live assistance call centers are currently closed due to the Coronavirus emergency.
See my Addendum in my next comment below.
