If the first and second stimulus were never paid by the IRS (from their past records) and never claimed by you on a tax return, it is too late to get the funds now. However, the statute of limitations for amending to get a credit is 3 years from the original due date, or two years from when you actually filed, if that was past the due date. So if you filed or have been in a dispute with the IRS, that 2 year window might still be open.
If the IRS believes they paid the stimulus to you (either as a separate payment or as part of your 2020 tax refund) but you never received it, you might be able to put a trace on it. However, that may also be past the ability to figure things out.
A trace might also be helpful if the IRS paid the funds to your bank, but the bank was unable to verify you and sent the money back to the IRS.
https://www.irs.gov/faqs/irs-procedures/refund-inquiries/refund-inquiries-0
You can also try the Taxpayer Advocate.
https://www.irs.gov/taxpayer-advocate
Lastly, if the problem is with the bank and not the IRS, you can contact your state banking regulators (part of your state government).
