Hebrews 9: 15 & The Extent of Atonement

"And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance." (Heb. 9: 15)

This is a difficult passage for those who believe that Christ redeemed or atoned the sins of every human being. Paul says that the sacrifice of Christ, his atoning and redeeming death, canceled the sins of people who lived and died before the death of Christ, who died under the first covenant. Did Christ redeem all the sins of all men who lived before his death, both those who died believers and those who died unbelievers? Did he cancel the sin debt of all OT sinners? Universal atonement advocates are forced to say yes. Thus, when Christ redeemed the transgressions of those of OT times, he redeemed all sinners, believers and unbelievers alike. But, why would Christ die for and redeem the sins of those who died in unbelief and were in Hell at the time of Christ's death? If there is no salvation after death, then why would Christ be dying for them? Obviously, those of the OT time period, whose transgressions were redeemed by the death of Christ, were only believers. The text says this redemption of transgressions of OT folks was in order that "they which are called (from either testament period) might receive the promise of eternal inheritance." To me the text says that the ones Christ died for, and who lived under the OT, were the believers, were they who had been "called." Christ did not die, for instance, for Pharoah, Ahab, Jezebel, etc. Why would he die for them if they were already in Hell?