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The Elder Scrolls V: Skyrim | PlayStation 3
My first piece of advice would be to get an enchanted weapon with fire damage or get a fire spell like firebolt. Second would be to let your companion take most hits while you attack from a far, try a bow out or spam the fire magic you have. Ice Trolls are weak to fire based attacks, it stops them from regenerating. So equip your companion with a fire enchanted weapon and let them tank for you. Then when your companion yields, gets down on their knees, you go in and finish the troll.
If that doesn't work go to options, game settings, and lower the difficulty a bit OR just ignore the Ice Troll OR leave and come back after leveling up a bit and getting better gear.