Assuming that you aren't mixing up 2020 and 2021, then I would suggest you print and mail a copy of your 2020 return (signed, use an mail service with tracking and proof of delivery.)
I almost never tell anyone to do this but I think its appropriate in your situation.
I am assuming you are expecting a refund and it was never paid. If you owed tax, is the IRS sending you a past-due notice? Hopefully it's not that.
There are some other things you can do to really verify that you filed and the IRS doesn't have your return. But if it was e-filed and it's not listed at least as received, then I don't think they have it.
- Did you e-file a state tax return at the same time? Did you expect a refund and did the state pay it? Since you can't e-file a state without a federal, that would confirm that you really did file a federal return.
- Get an online IRS account and look at your account transcript, your wage and income transcript, and tax return transcripts for 2020 and 2021. Your 2020 transcript should show your wage and income statements (W-2, 1099, etc.). Your account transcript would show if the IRS received a 2020 payment (if you made one) and it would show a refund (if a refund was authorized, even if you never received it due to a glitch. That would be another way of confirming no refund was paid.
- Your tax return transcript for 2020 might be blank, or it might contain a computer-generated tax return made by the IRS from your W-2s, which they sometimes do if you never file yourself.
