We have to remember that the different religions provide symbolic representations of the suffering of hell. Although there are literal elements of a highly disturbing nature, they more accurate reflect states of consciousness. Therefore, when we read The Divine Comedy, The Qur'an, or the Buddhist scriptures, we have to see the psychological and spiritual implications within the various torments of the abyss, more than a literal interpretation (but yet again, there are very literal elements describing such torments which are horrifying).
Beelzebub is a remarkable case, but his repentance demonstrates that profound change is possible even in the worst of circumstances. What it takes is tremendous will, patience, and love of God. Although Beelzebub was awakened in evil, he had not yet begun the process of disintegration within the eighth and ninth spheres of hell, since he was to still pay his karma in the upper layers of Klipoth.
Remember that it is only in the lowest regions, the eighth and ninth spheres, where the lost souls undergo the putrefaction and crystallization process leading to the Second Death. Before that point, karma is paid through suffering in the above mentioned regions, which reflects the psychological level or level of being of the soul corresponding to a particular sphere within the abyss.
Beelzebub was yet to disintegrate in the lowest spheres of hell. Since he accumulated so much power in the ego, the karmic repercussions were to be paid gradually throughout the soul's transmigration through hell. This is the case with many demons from the past age; they have acquired so much karma and ego that it takes cosmic days for them to fully exhaust their debts before they become eligible for disintegration. Beelzebub had repented before his karma could be exhausted and his soul sent to disintegrate within the ninth sphere, a scene that he was horrified to behold when it was presented to him by the Venerable Master Samael Aun Weor.
Joyful in hope, suffering in tribulation, be thou constant in thy prayer.
Benedictis, qui venit in nomine Domini. Osanna in excelsis.
"Blessed is he who comes in the name of the Lord. Hosanna in the highest!"