property damage due to flooding

I need to know the state statute that addresses flooding caused by stormwater run off from my neighbors downspouts. I have provided the insurance company statements from two landscapers and an engineer stating that it is thier water creating the problem, pictures of the area and pictures of their gutter on the north side of their house which appears to be adjusted so the majority of the water from their roof comes our way. Something they most likely did after they were flooded and had landscaping done. An explaination from a hydrologist explaining what happens when the water percolates down, a calculation from a math professor as to how many gallons flows into this area over the course of a four day storm. And a detailed history of the flooding occurances we have experienced. The neighbor redirected his runoff from this area from 1996 to 1999. Then decided it wasn't his water creating my problem and allowed the water to go where it did before. Then we were flooded again. The insurance company denied our claim and said our basement wasn't adaquatley waterproofed and the neighbor didn't think it was his water creating our problem. But then thier lawyer tells me if I landscape to create a divertion for his run off I have an obligaiton to consider any impact my landscaping would have on them. I guess I need to know how to present this case so the insurance company will take me seriously. Any help would be appreciated. Thanks