Waiting for tax refund for almost two years

Hi 

My 2019 tax was filed in 2020 by snail mail. I am still waiting to get a refund. I tried calling IRS several times and the automated voice always responded with "there are too many called at the moment, please call back another day" 

IRS website was not able to pull up my record. 

 

My concern is: if the return never reached IRS, would I fall into the situation that I didn't file and will never be able to receive the refund?

 

I am hitting a wall in moving it forward. Could someone advise good steps to take? Thank you!