I amended my return for 2018 by certified mail in May of 2020. I have not heard from the IRS nor can I call them. Is there another way to obtain info about my refund?

Sorry the IRS has limited staff due to Covid-19.  They just started opening the mail in June that's been stacking up. Back in March the IRS closed their processing centers and stopped processing mailed tax returns.  An IRS spokesperson recently said that they have about 11 million pieces of unopened mail.  The IRS says....."We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it."  So it may take longer if you mailed in June or later.   So you have to keep waiting.

See this IRS page for the latest information

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue

Then once they start opening the mail, After 3 weeks you can track it here,    

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1

I mailed my amended 2018 return in June 2020.  As of 1/1/21 the IRS website shows no indication that they processing it, let alone received it.  They only say do NOT re-send it.

So frustrating.....