Unfortunately, you cannot write off the $20,000 that you are not going to receive.
However, you can file for your refund for the "open years before April 15 2021. The open years are 2017, 2018, 2019, and of course, you need to file your 2020 return.
Yes, there is a 3 year statute of limitations on getting a refund from filing a prior year return and receiving the refund.
You need to first file the 2017 return because the 3 year refund statute of limitations will expire on getting that refund on April 15, 2021.
Then, you will have until :
- April 15, 2022 to file for a refund on the 2018 return.
- April 15, 2023 to file for a refund on the 2019 return
Here is a link with additional information:
3 year refund statute of limitations for filing the return
