How to deal with neighbors who use geomantic omen to harm people?

You don't have to deal with it. What you are is Feng Shui, which has nothing to do with how others are. You are your own feng shui, be yourself. First of all, when chanting Buddha, there was no Amitabha in the south. This name is all good, and good is the result of good. If you read Amitabha in the south, you will be blessed by Buddha, and no one will harm you.