I had the same problem. I started to doubt my gaming skill. I tried for like 25 times. I wasted my ammos, health packs to kill that beast. Then I remember I had the same problem with Dead space 2 and only solution I got that time was to lower the graphics option. So I gave it a shot in Dead space 3 also and it worked. If you haven't found any solution and haven't tried this solution, then try it first. If your problem is solved then its good, otherwise you have to wait for a better solution.
Me and my friend were trying to beat this level for literally 2 days and still nothing, it breaks free nonstop no matter what happens and it bugs out like he said the harpoons say it's binded but it's not it can still move about nothing works I'm close to giving up on this game. :C
