So I've noticed when your fighting alduin..and say you die then it takes you back to the last checkpoint and when you fight him again he's immortal...it's so stupid and they should fix that bug in the game

He is not immortal for me, i have died a huge amount of times to him (thanks to Deadly dragons) and he was never immortal.

Also, Bethesda is not fixing anything anymore, they are done with Skyrim.

Welcome to the forums BTW, here is your complimentary http://images.uesp.net/c/c4/Fishystick.jpg

Do you mean the first time you fight him?

Or the second? cause the first time, he's immortal.

It's a well known bug on the 360, the only way round it is to reload a previous save and then make sure you take him down first time.