First check to see if the IRS issued the checks ... if they did then have a trace put on them.
Try checking your online account with the IRS
https://www.irs.gov/payments/your-online-account
If you need to trace a payment that the IRS says has been issued to you, mail or fax a completed IRS Form 3911, Taxpayer Statement Regarding Refund.
If no payments were issued then you must file a 2020 tax return to get the stimulus credit for the missed payments.