And his lord was wroth, and delivered him to the tormentors, till he should pay all that was due unto him.
Matthew 18:34 KJV

"Tormentor" in this verse is an officer of the court. Being "delivered to the tormentor" means being put into the custody of that officer. Other translations render it as "jailor".

This is essentially the same meaning as being placed "under the law". When you read that phrase in Paul's letters, he is talking about this concept: being placed under the authority of the law to punish, not being obligated to obey the law.