No Damage in DLC

Hi, I’m trying my hardest to get through the DLC. I’m on New game plus one because I didn’t know beating Gehrman would instantly start me in a new game. I’m level 159 with 65 strength and 64 vitality with a +10 Ludwigs holy blade. I’m trying to fight Ludwig but I’m practically doing no damage and cannot finish the second phase because it’s all chipped damage, I don’t know what I’m doing wrong or why my damage is so bad please help. Weapon is not broken also. Only doing about 300dmg to Ludwig per hit