Sigh....Outside of a momentary satisfaction, I'm afraid that it wouldn't do any good at all, Annie. : /

What might do some good is to make a clean cut farther down, at a slight slant so water drains off. After that, give it a mild feed with something slow, such as growmore, and hopefully it will send up new sprouts from the ground level. Be sure to protect these sprouts well from freezing this winter, since they will be more vulnerable coming out this late in summer. If you are in a more northerly coastal area, you might want to wait the feed until spring, and hope that the stump is willing to wait also.

i DEFINATLY would not let my nieghber do that . its totaly out of order . if hes councel i would definatly make a complaint in very strong terms . i would definatly go see a soliciter and maybe take him to a small claims court . he or she had know right on this earth to touch any part of a plant not hanging over there garden . i would definatly take it further . i would swear on hear but i have manners lol . what a f&%$£*&g t"£t excuse my french . its looking like he had to be on your property to do that which constitutes breaking the law . i would go to the police and take further action before he digs your lawn up or bricks up your windows cheeky t*%%er . that is bang out of order . i bet a plant that size to buy would be worth a good few 100 quid .dont leave it or he will walk all over you as he as far as im concerned already has . sorry but as you can tell im very annoyed . if you live in or near thetford let me klnow as id like to give them a piece of my mind and i havnt got much to spare lol . take care bye for now x .

Couldn't have put it better myself NP!

Why did the neighbour cut it down?

This counts as Criminal Damage - your neighbour is only entitled to remove any parts of the plant overhanging his boundary, and is not entitled to come into your property and savage your plant in this manner.
However, if you want to try to save it, do as Tugbrethil (first response above) suggests.

great minds again bamboo lol x .

True! True! Slap, no, but legal action, yes! Not living in the UK, I concentrated mainly on the practical details of what to do with the plant now.

your right as far as the plants concerned tugbrethil ofcourse bye the way as thats worth remembering to x .