I've completed the main quest up to Parthunax teaching me Yol. The only shouts I can use are the ones given to me by the Greybeards (and Parthunax).

I have killed and absorbed the souls of n dragons. I have seen several word walls. At first, I thought the problem was that I wasn't learning the words in the right order. But then I learned the shout to call Durnehvir, with all the words, but I can't unlock it.

I can't seem to unlock a single shot. I click on the shout in the magic menu, and it tells me I need dragon souls to unlock it. Well, I've absorbed a ton of dragon souls, and it still won't let me unlock the shots.

I'm at a loss. What am I not doing? What step am I missing? I'm going to verify file integrity, but I doubt that's the issue. I think it's just one of those idiot moments where the answer has been under my nose the whole time. Any help would be appreciated.

Are you on PC? To unlock a shout you need to press "R"