I know it sucks but if you’re neighbor’s house flooded specifically because of irresponsible levee management, the insurance company is assuming that’ll it’ll happen to your house at some point as well.
You might be able to get an adjuster to come out and look at your house to see how much higher it is, but I doubt that’ll make a difference, the actuaries made a map and that’s that. If the city ever upgrades the levees, that might change things. You could try getting quotes from other companies**, but, again, I don’t know if that’ll make a whole lot of difference either as they probably all work off the same map, however, another company might not know what happened to your neighbor’s house and, technically, neither do you. You certainly shouldn’t be offering that up.
BTW, I assume the water came in through their walls/floors/foundation, right? If it came in through their drain, you can put in a backflow preventer* and probably get the insurance lowered again, but you’d have to decide if the cost is worth it. They cost a few grand to install since it involves tearing up your concrete basement floor.
*Also sometimes called a ‘fuck your neighbor valve’ since, for each house the sewage can’t enter, it rises higher in all the other ones. You’re essentially displacing your entire basement’s worth of sewage and it’s going to go somewhere.
**Something else to do is just to call and play the ‘what’s going on with my rates?’ game and ‘are there any discounts I can get’. From time to time I can get my rates back in check that way. Also, if you work at a smallish business and you want to get some quotes, ask the boss who they use for business insurance and call them, specifically, call their broker. Not to tag on to it, but starting out with “Hi this is ____ from _____” as soon as they recognize the business name, tell them you’re looking to get a homeowners (car, umbrella whatever) policy. Since they already have a relationship with your company, you might be able to get a better deal. Also, it’s often better to work with a broker, which is probably what your business does, and that might get you even better deals then doing it by yourself.