if you were due a refund for 2019 and filed in March 2020 you should have received it by now. i would suggest that you try to see if the IRS has a transcript of your return.
https://www.irs.gov/individuals/get-transcript
if not, it's likely they never got it. in that case I would mail in a copy using a method where you get proof of delivery. if there's a transcript see if the IRS changed anything. if not
see this link for following up on lost refund
https://www.irs.gov/faqs/irs-procedures/refund-inquiries/refund-inquiries-0
