I have a neighbour who had let a climbing plant/small tree? (Not even sure what it was,she has all sorts on other side of tall fence) grow & snake its way up my drainpipe and wrapped itself around my sky dish.it had gone off & my equipment insurers sent a cable guy, who had to hack some back& shouted over fence to her to get it trimmed- she pretended not to understand as they're chinese (but some of them have chatted to me&sent xmas cards in english) she let it grow back again this year,so last week my sons reached up on a step ladder& hacked a good bit back,it fell over her side.it had rooted itself in my 'leaf catcher' attached to drains, and wrapped around sky dish again! Theres usually a call-out charge if the guys to come for that so i was lucky he'd put it down as a 'reset' last time.or id have taken her the bill. BUT, as for your neighbour, he shouldn't have arranged its pick up without asking you first if you would pay towards it, if its a high price, and £100 seems a lot- has he even shown you the bill?? If not or he wont, then id tell him no- if he showed me it and its genuine, then id offer him £50, as its only half& half on your properties- & tell him next time you will get tree surgeon to trim his& remove debris.(or could you get tree surgeon back this year to try sort out your side so it 'trains' it to grow away from his side more? Or cut so much down from your side its not an overhanging problem any more, then put some form of fencing high on that bit next to the bush, to push it back towards your side over time? 