For your rights at debt cancellation, discharge, and forgiveness, see HERE.
Because this is a government backed loan, it has no statute of limitations. This means the debt may be enforced even now. However, the interest rate is calculated at the amount the contract mentions, or if it is silent on this, then 9% at most, from the beginning of the default. See CPLR 5001 et seq.
Unfortunately, Social Security money is subject to garnishment if the debt is the government.
I am afraid that there is really very little wiggle room here. Negotiations are always possible, however, if they know that they can dip into your SSA money, then they may be not willing to negotiate as much unless you pay everything up front, for example.
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