Who is responsible if our connecting neighbors tapped into our electricity and tripled our bill?

Our bill has tripled from last year. We started wondering how that is. This started 8 months ago we contacted our electric company. They said there isnt anything wrong with our meter. And if we send someone out we charge you 75 dollars. Then i contacted our property management they didnt do anything. Time goes by are bills are higher. So now that im on vacation i called the electric company they told me to turn off the breaker to the wall thats attached to our neighbors for a couple of days. So i did. I talked to them after a couple of days, they tell me that there is no spike in usage When we shut the breaker off on that wall. But we continue paying our high electric bill. And the electric company wont do anything about our back overpayment. 400 over payment for 8 months.