The IRS will not tell you if someone used your Social Security number or claimed you as a dependent. But you can file a 2020 tax return and use the recovery rebate credit to get the 1st and/or 2nd stimulus payments ---- and later you can get the 3rd one which is released on the IRS's own timetable. If your e-file is rejected when you try to e-file and it says the SSN is a duplicate----then print, sign and mail your return. That way the IRS will process your return and sort out whether someone else used your SSN.
The stimulus check is an advance on a credit you can receive on your 2020 tax return. If something went wrong or you did not get the stimulus check in 2020, you can get it when you file your 2020 return in early 2021
The Recovery Rebate Credit will be found in the FEDERAL REVIEW section. ( you should see "Let's make sure you got the right stimulus amount”) If you are eligible it will end up on line 30 of your 2020 Form 1040.
Make sure that you enter ALL of the stimulus money received for the 1st and 2nd stimulus for yourself, your spouse and your children.
https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing
Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.