Can a law firm that specializes in collections seize money from your bank account and then garnishee your paycheck for the balance owed does double jeporday apply in this case?

Double jeopardy does not apply. That only says you cannot be tried twice for the same crime. A debt on the other hand, is a debt. It has to be repaid, and if a law firm really wants to pursue it, then yes, they can attach your account and your wage.

Added; Unless the garnishee privilege was written into a contract or agreement you signed when you made the loan, they would have had to go to court to get a court order to garnish your wages or attach your bank account. If none of these occurred, contact an attorney. You would most likely have grounds for a serious suit against the lender, the law firm, and the financial instituion that gave them unauthorized access to your accounts.