You probably have no taxes withheld from your SSDI check; withholding from Social Security checks (including SSDI) is optional and rare. (If your SSDI check is your only source of income, it's probably not taxable.) And since you're single with no earned income, you don't qualify for refundable credits like EITC or ACTC. Since you have no withholdings and no refundable credits, you don't get a refund.