Kia ora

For crying out load guys why did you not put some in game dialog in to let PC players know to talk
to said beast twice

I got given all three words at the first dialog (bad scripting I guess) and left the Cain now I can't summon (if I need a spell
school at 100 to use the shout, theres no heads up about that either

How do I do

"Each time you do so, he will teach you another word,...( spoiler cut out )
Each word will require a Dragon Soul to learn, as if it had been learned from a word wall."

Is there a fix for this for us past stage 200, (I'm guessing that about where I'm at)
or do I have to console those shouts in

No it IS working, but it just wasn't explained well. You get all words, but you have to unlock ALL three of them with Dragon Souls before you can actually summon him. And THEN you can summon him three times to get the full words of another shout. Pretty confusing, I thought it was a bug too.

I have unlocked them (used 3 souls)

but the shout doesn't work at all, just a dull miss fire

make sure the target(crosshair) is pointing at the ground pretty much right in front of you. this threw me for a loop as well as i was thinking, "summon dragon, look at the sky", but in actuality it functions like a general summon creature spell with very little range.

I remember that he said something like "shout my name to the sky"....

Eeyup, very confusing, because you must shout it at the ground.
The rest of the quest (learning the other 3 words) is pretty much autopilot.

Kia ora

Thank guys,. thats sorted it