You don't say if you continue to be disabled or not, that can make a difference. The notice you received telling you of the overpayment of benefits should also have informed you that: (1) you can contest the amount of the overpayment and (2) you can argue that it wasn't your fault the overpayment occurred and that you can't afford to pay it back & still meet your ordinary & necessary living expenses. Some notices will also tell you that if you request reconsideration (appeal) of the overpayment w/in ten days of receiving the notice, your benefits will continue until SSA has made a decision on the appeal of the overpayment. Read the notice you received carefully and pay attention to the date of the notice and any deadlines mentioned in the notice.
If you are no longer receiving disability (SSDI, not SSI) benefits, then SSA cannot collect the overpayment, unless it sues (see below). If you begin receiving benefits again (SSDI or retirement benefits) SSA can again start collecting the overpaid amount.
If you do not take any action (such as that listed above) then SSA will deduct an amount from your disability benefit to start repaying the amount SSA says you owe.
Sometimes, if the amount is large (as it is in your case) and SSA believes there was fraud involved (your question offers no information on that issue), SSA may sue. If a judgment is obtained, then it may be (I am not sure) a lien that can be attached to federal income tax refunds, etc.
I strongly suggest that you seek legal advice & assistance as soon as possible, if possible an attorney who has experience in Social Security law and is in your area. If you are low income, you may be able to obtain assistance from the Legal Services ("Legal Aid") office in your area/state.
This is general advice only and based on the information provided, which may be incomplete. The information provided does not create an attorney-client relationship between the asker of the question and the attorney responding to the question.
I'd be curious to know if they are alleging fraud on your part. You should consult with an attorney to assist you on this matter.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.