This is hogwash. The Christian version of "hell" does not exist and those beings who told you that are not Demons, but enemies of Satan a.k.a. "angels". Our Gods do not support the Christian worldview and they will not "confirm" such things.
If you are someone who knows some basic facts about human biology you can see how retarded their Christian hell is: a soul without a physical body cannot feel pain. Pain comes from the nervous system and the brain. People who are immolated and burn in a fire feel extreme pain for 2-3 minutes until the fire destroys their nerves, then they feel no more pain until they die. But in contrast, people who are scalded by smoke feel pain all the way until they die because smoke doesn't destroy your nerves. If Christians wanted to make their version of hell more accurate they would describe it a place of scalding smoke instead of a lake of fire and they would make it so that you still have a physical body and you are not just a soul which cannot feel pain.
But even that would have its problems because there are even people who cannot feel any pain at all since they have a very rare condition called "congenital insensitivity to pain":