I think that was illegal for him to do that...you should check with your city

You have property rights and in most places, a neighbor cannot do something drainage-wise that negatively affects one of their neighbors. For example, a neighbor can't concentrate and redirect the flow of their water onto your property. Neither can they stop the natural sheet flow of water coming onto their property. If, in fact, this is what you think they did, then it would be in your best interest to speak to them about it. If that's not satisfactory, consult with competent legal advice.

But before you go off accusing anyone of anything, you should actually find out and document with video (if it's someone else's fault) exactly what is happening with storm water in a heavy downpour. It will be obvious and documenting it will help immensely with making your case.

Um... that's one way to handle it. And then your neighbor's yard floods, he goes to the city or county, and guess who the bad guy is? Probably not him. If you don't want to deal directly with the neighbor, go down to your building office and explain what's happening and that you want them to send someone out (ideally a staff engineer if they have one). Then at least it's documented.

Actually, legally he is the bad guy because he changed the grade on his property and disrupted the natural flow pattern of any runoff. Before he installed the pavers and added little walls around the trees that are in the corners of his property, any runoff would go to the side of my yard where the drains are. Now it just dumps into my pool.
I did talk to him. He doesn't care.
My property is twice the size of his, so if we add to our retaining wall his water runoff will be diverted to our side yard anyway which is where it should go. How fast it will leave his yard, I don't know.
I'll check with the building dept and see if I can get an engineer out here.

Marcinde gave you excellent professional advice.
Before 'compounding' the problem have it properly documented in the correct stages.
Contact the city first.
Then if you decide to build up a dam / wall and the water backfills or even ever so slightly impacts your neighbors property you will have an inspection report prepared by the city, which will ( pun intended ) hold water if your neighbor decides to take you to court .

.. been there, done that, .. it pays to go thru the proper process channels.

Thank you both for your responses. I can see now where it would pay for me to go about this the correct way. I'll go through the city first and see if they can help. I'm in ny so I'm not expecting much help from them, but maybe they'[ll surprise me.

my neighbor changed the property grade and also put pipes in and got away with it. I think he paid off the city. He then put more pipes in and has pipes under his porch and has gutters hidden under ground. when it rains we get a pond in our yard. We have tried everything, the man is insane. He lies to the city and they believe him and we have sent pictures as proof. What else can we do???????? HELP!!!!

Cindy, It could possibly be a question for this forum, but you'd ask it by starting a new thread, not adding on to an old thread, as the issues would be confused and confusing.

Also, it's unlikely that everyone will accept claims you make without demonstration. You'd need to clearly show in pictures the conditions and overall lay of land of the pertinent area.