A call from a federal agent takes this beyond a routine account dispute. You need someone who understands how investigators connect wallet activity to a person and how exchanges handle government requests. You can hire a cryptocurrency lawyer here https://arkadybukhlawfirm.com/practice-areas/cryptocurrency-and-crypto-law/ . Tell the attorney whether you received a subpoena, a seizure notice, or only a phone call. They can work out whether the government views you as a witness, a subject, or a target. That distinction will shape the response and the attempt to recover the frozen funds.