"not happy" said:

Problem is, every morning we go outside & have to shovel up several
fresh cat turds. The woman next door has about half a dozen of the
little vermin ..... & being as her garden ( our our neighbour on the
OTHER side) is completely concreted over ..... her pests use our soil
as a kitty litter.

Call animal control. You are making this YOUR problem, your neighbors
chose to keep these cats, make it the neighbor's problem.
--
McQualude