Ok, so I fight miraak the way I should but I end up getting the soul not him and he stays unkillable

Not sure what you specifically mean by "unkillable", i.e. does he become etheral and so takes no damage? Or do you mean he is unkillable through some other means?

There does seem to be quite a few bugs with the Miraak battle. Gstaff has posted a few common problems and their solutions in the following link (you will need to scroll down and look at the last post he made);
http://www.gamesas.com/topic/1426775-starting-dragonborn/

If you are saying that Miraak becomes unkillable by becoming etheral, then the following quote from Gstaff's posts may be helpful to you;

ISSUE: Miraak will rarely get stuck in an ethereal form during “At the Summit of Apocrypha” where he will take no damage.
RESOLUTION: This issue can sometimes occur if the player makes many attacks very quickly or does a very large amount of damage in a single attack – the player should try reloading a save prior to the issue occurring and try the fight again.


As the following thread also suggests, it seems like quite a lot of people are having similar problems with Miraak.
http://www.gamesas.com/topic/1427684-miraak-glitch/
Note to developers: It would be good if the next patch fixes at least some of these common problems...

This same problem was occurred for me and it's very annoying. He stands in the middle eternal an unkillable and I absorb the dragons souls. As far as I know there are NO fixes for this, just hang in there for a patch.

Same problem im gonna have to try my level 81 cause most dragons I kill as him never give there soul.

I also have run into this problem several times, I show how to fight him on my yt channel, this may help, mplsmnpi.