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
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.
I think the easiest first step is to call the EIP Card number (see link below). If they issued a card and it was not used, I have heard that they will just send you a replacement.
If that doesn't work out, then follow the directions that Critter gave you above.