Best to give it another dab of rooting powder ( or use custard powder ) then repot. It is obviously still alive. This happens quite a lot with hardwood clematis cuttings. Top growth looks to be romping away but new roots take much longer, best not to disturb them if possible.
People like your neighbour, in my opinion, want to argue, shout, swear, and it hurts them much more if you rise above it and let the legal bods sort it, believe me it is worth every penny.
I have had experience of boundary and drainage dispute with my neighbour, my advice is NOT to take the law into your own hands. It is obviously illegal the action your neighbour has taken. Take advice from a local reputable solicitor and let them threaten your neighbour with court and costs and damage to your property.
Moerheim Beauty is one of the best. I grew some from seed, supposed to be Autumn Tints, all were yellow when they flowered, and tall. Named cultivars are best in my opinion.
We managed to keep ' Ken Aslet ' for a few seasons, then it succumbed to the Winter wet. Lovely plant.
Look on here at the bean poles and arches. Class.
Clematis John Treasure and Hagelby Blue also grow up hazel tripods.
Also we use lots of tripods made up of hazel twigs, this is how this clematis Elvan is supported.
We use the Gardman Parisian as shown in your pics, Marlorena, 3 different sizes, excellent quality, ideal for clematis / rose combos.
Good picture of your clematis x durandii, 2nd picture, excellent clematis.