A.T. Robertson Commentary Matthew 18:34

"And his lord was wroth, and delivered him to the tormentors, till he should pay all that was due." — Matthew 18:34 (ASV)

The tormentors (τοις βασανισταις). Not to prison simply, but to terrible punishment. The papyri give various instances of the verb βασανιζω, to torture, used of slaves and others. "Livy (ii. 23) pictures an old centurion complaining that he was taken by his creditor, not into servitude, but to a workhouse and torture, and showing his back scarred with fresh wounds" (Vincent).

Till he should pay all (εως [ου] αποδω παν). Just as in verse 30, his very words. But this is not purgatorial, but punitive, for he could never pay back that vast debt.