What the Bible says about Torturers
(From Forerunner Commentary)
Ultimately, receiving God's mercy and compassion is contingent upon our forgiving treatment of others. The word "torturers" or "tormentors" (KJV) probably means "keepers of the prison." Torture by various cruel and painful methods was usually inflicted on criminals, not on debtors. Jesus probably does not intend to suggest torture but only that the servant would be imprisoned until he paid his debt.
Martin G. Collins
Parable of the Unforgiving Servant