Inferno Cantos 27-34

As I was reading cantos 27-34 from Inferno I was shocked by those torches sinners face with in eighth circle. I found it one of brutal scenes from the hell. In this part of the circle sower of scandal and schism are punished. AS They walk as a circle they are wounded by devils continuously. Dante meets Mahomet who is a founder of Islam. He is in hell, is being punished. I found it strange because according to Quran which is holy book of Islam, he is very respected by Muslims and he is treated as a greatest in the religion, obviously he is a profit. Also, in Islam Muslims follow his footsteps.
There is also Bertan de Born in this circle. He is being punished because he advises son against his own father which is one of the worst sins. And his punishment is that his head is cut off and he carries it with his own hands. I think this is really fear or suitable punishment for him, because he makes son to go against his own father, and he is carrying his own head.