From Challenges in Recovering Supplemental Security Income Overpayments, a report by Social Security's Office of Inspector General (OIG):
... SSA made errors on overpayments for 189 (47 percent) of the 400 sampled SSI recipients because it did not follow policies or use all available tools, to prevent, detect, or recover SSI overpayments. For example, overpayments could have been prevented or detected earlier, but employees made errors when they redetermined SSI eligibility. A redetermination is a review of a recipient or couple’s non-medical eligibility factors (that is, income, resources, and living arrangements) to determine whether the recipient or couple is still eligible for, and receiving, the correct SSI payment amount.
Errors also occurred because employees did not always (1) send recipients complete and accurate due-process notices before they initiated recovery of overpayments; (2) follow policy when they processed waivers of overpayments; or (3) follow policy and use available tools to recover overpayments. When SSA identifies an overpayment, it sends the overpaid person written notification of the overpayment’s cause and amount. Overpayment recovery can begin 60 days after SSA notifies the recipient of the overpayment if they have not requested a waiver of the overpayment collection or a reconsideration of the overpayment facts. If the individual is receiving SSI payments, SSA should begin recovery by withholding from ongoing payments. If the individual is no longer receiving SSI payments, SSA should attempt collection through various means including withholding from ongoing payments to a liable representative payee or spouse, cross-program recovery, referral for external collection through the Department of the Treasury or pursuing recovery from estates.
We estimate SSA did not follow its policies or use all available tools to prevent, detect, or recover SSI overpayments for 1.9 million recipients. For 1.7 million of these recipients, we estimated error amounts totaling over $7 billion. ...