Oh dear, sounds as if the root stock has taken over from the graft at the top - the root stock isnt the same plant, the 'contorta' bit is grafted onto ordinary corylus rootstock. If all the growth is straight, with not even one branch that's twisted, then chances are your contorta is a goner, and all you've got left is the rootstock. Replace, if that is the case and next time, remove immediately any shoots which appear straight.

Thanks for your answer. I've just cut out all the straight growth, as you suggest. There is one single twisted branch left, but it's very brittle. Fingers crossed it will survive. May need to replace it, as you suggest. Thanks once again.