Please help I'm on SSI and my son claimed me on his taxes now I can't get a simultaneous check

To remove you as a dependent he will have to file a 2019 federal amended tax return, Form 1040X.  He would have to pay back the $500 Other Dependent credit he received on the federal tax return for claiming you as a dependent.

If he amends his tax return, you will not be able to apply for the stimulus payment until after his 2019 amended return has been processed by the IRS.  In a normal year the IRS takes about 4 months to process an amended return.  Due to the pandemic and limited staffing the IRS is taking much, much longer to process paper tax returns.

you could be his dependent and therefore he properly claimed you.  here are the rules.

you are a Qualifying Relative and hence his dependent if

• your gross income for 2019 less than $4,200
• he provided over ½ your support

now let's try to clarify something.  SSI is technically supplemental security income and not the regular social security benefits.

If you were collecting SSI, you cannot be claimed as a dependent. The gross income test under the Qualifying Relative rule is $4,200 excludes ONLY non-taxable Social Security. SSI is NOT Social Security even though it's not taxed. If you were collecting Social Security and it was your only income it's not taxed so you meet the gross income test under the Qualifying Relative rule.