Still have not received my 2020 tax refund

I filed my 2020 taxes in March 2021.  I was required to paper file it instead of e-file.  I am owed a refund.

In late June I received my return back, rejected because I forgot to sign it.  I sent it back signed the next week but failed to get a tracking on it.  It has not come up in Where's My Refund.  I have been able to get through twice to the IRS, only for them to tell me that they have no record of my return, but not to worry because they have millions of returns that have not been even started so they don't show in the system.  They said both times not to resend a copy because that will start everything all over again and it will go to the bottom of the stack.  I am getting ready to transmit my 2021 returns but worry about my 2020 taxes and if there is anything I can do to find out if they have been received.