Still waiting on Federal Return after 3 months

My taxes we accepted Feb 15. I received my State refund quite some time ago. My federal still has not come and today is May 7.  When I call ANY of the IRS numbers given to me, I only get a recording stating they are not accepting calls due to the Covid-19 issue. I also sent an overnight letter to the IRS in early April and have heard nothing back.  The tracking website continues to read, "still processing". 

 

Any thoughts on how I can move this along?  I've read some other forum comments about contacting a tax advocate. Is it time to do that and how do I go about finding one?