Send them a cease communication notice under FDCPA 805(c).
That will prevent them from any further communication with you.
If the asserted debt is that old, it is past the credit report exclusion period, so it cannot be added to your credit report, and also likley past the SOL for your state, so they cannot initiate legal action.
You have the authority, at any time, to instruct a debt collector to cease all communication with you.
Attachment of assets to recover a debt requires that the party first obtain a civil judgment finding the debt to be valid and ordering its payment.
The judgment is then basis for seeking an additional order of the court for specific payment of the judgment, such as attachment of assets or garnishment of pay.
If the SOL has expired, they cannot obtain a judgment, regardless of any factual issues of validity.