it is they on whom is the curse of Allah and of the angels and of mankind, combined. They will abide therein (under the curse in Hell).
Therefore, they will suffer the eternal curse until the Day of Resurrection and after that in the fire of Jahannam,
لَا يُخَفَّفُ عَنْهُمُ الْعَذَابُ
their punishment will neither be lightened,
Hence, the torment will not be decreased for them,
وَلَا هُمْ يُنظَرُونَ
nor will they be reprieved.
The torment will not be changed or tempered for even an hour. Rather, it is continuous and eternal. We seek refuge with Allah from this evil end.
Cursing the Disbelievers is allowed
There is no disagreement that it is lawful to curse the disbelievers.
Umar bin Al-Khattab and the Imams after him used to curse the disbelievers in their Qunut (a type of supplication) during the prayer and otherwise.
As for cursing a specific disbeliever, some scholars stated that;
it is not allowed to curse him, because we do not know how Allah will make his end.
Others said that;
it is allowed to curse individual disbelievers. For proof, they mention the story about the man who was brought to be punished repeatedly for drinking (alcohol), a man said, "May Allah curse him! He is being brought repeatedly (to be flogged for drinking)."
Allah's Messenger said;
لَاا تَلْعَنْهُ فَإِنَّه يُحِبُّ اللهَ وَرَسُولَه
Do not curse him, for he loves Allah and His Messenger.
This Hadith indicates that it is allowed to curse those who do not love Allah and His Messenger.
Allah knows best