If the service was valid (whether it rectified the issue or not) and you were part of the group when it was undertaken and none of it was before you gave notice to remove yourself from joint liability then, yes, it's perfectly in order for you to be billed four months after the event and you are liable for it.
There may be perfectly valid reasons for the delay. Perhaps a contractor was attempting to find other ways of solving the problem and had not yet issued a bill for the full costs to date. He may then have been asked to issue an account to be split on your departure from the agreement and taken many weeks to actually do it. It's not that unusual.
If you feel that the work may actually have been work done after you requested to no longer be involved and it isn't work that could no longer reasonably be stopped after you requested it, then you'll need to take it up with the neighbour in charge I guess. But if there's no quibble about the work actually having been done at the time you were involved then the time span in actually invoicing it is irrelevant, you are liable for your share.