Get a lawyer to write a lawyer's letter

to warn them for a lawsuit if them do not stop what they are doing immediately. If they do not, you should be ready to spend money to sue them. I don't think it is a small claims court issue. You should sue them for millions of dollars. As far as the cause of action, you need to talk to a specialist.

If you have a broken car, you need to spend money to fix it. Now you have a bad neighbor, you need to spend money to fix them as well.