How should I do unwanted device?

I have serious hacker issues with one (or more) of my neighbors. I've already reported this to the authorities and my financial institution but they keep getting into my wifi and mess around with all different factors such as changing administrator user, passwords, etc...it's bad. I purchased a program to help protect mostly everything on my desktop but it doesn't cover the router, cell phones, etc...which I was told (by a supposed tech expert) that the only way to protect everything is to get another/better firewall (anti hacking capability). Well, to make a long story short, I am working on that but I am disabled, so I have a fixed income (limits what I can and can't do) but I wanted to know (before I purchase this app) is how to delete unauthorized users and if they will stay gone once you delete them?