I filed by mail on March 6, 2020 with certified mail return receipt. I received the receipt but have heard nothing. I check my IRS account and "Where's my refund" Again, no information. What can I do?

I filed by mail on March 6, 2020 with certified mail return receipt. I received the receipt but have heard nothing. I check my IRS account and "Where's my refund" Again, no information. What can I do?