My 2020 tax return is stalled. My IRS Transcript has a 150 code on 7/5/2021 and no action since then. Who can I call, what does this mean?

I finally got thru to the IRS on 12/2/2021 with a phone number on the IRSgo2. They said a notice has been sent out which I never received, no communications were listed on my IRS acct. Last entry was Code 150, Cycle 20212404 dated 7/5/2021. The Rep said she would have the agent reach out, which they haven't. What do I do now?