Generally, Social Security benefits are exempt from execution, levy, attachment, garnishment, or other legal process, or from the operation of any bankruptcy or insolvency law.
The following benefits are exceptions and subject to garnishment:
(1) to the authority of the Secretary of the Treasury to make levies for the collection of delinquent Federal taxes and under certain circumstances delinquent child support payments; and
(2) to garnishment or similar legal process brought by an individual to enforce a child support or alimony obligation.
However, you should check with a lawyer in your state to make sure there are not some local laws that affect your situation. I cannot say with certainty that your social security cannot be garnished, but generally speaking it shouldn't be garnishable.
I agree with Mr. Floyd's assessment of the situation and would also add,
Start keeping a detailed log of all calls and letters. You should also demand in writing all communications from creditors is in writing.
Do not give them any personal information because that is how collectors decide on which accounts to recommend suing.
If you are going to make payments use money orders and not personal checks or “check by phone” because if they find a bank account the collector will be more likely recommend a lawsuit the their legal department. Get written confirmation of any payment plan the agency will accept.
I do not practice in your state and you will need to consult with a local lawyer for protection under your state law.
I have pasted a link to the FDPCA to help you with your federal rights;