Any time you want you can check if power is being stolen by turning off all of the breakers to your house. There should be one breaker box that feeds 220V to your house after the meter. Turn all of those off. Nothing should still be on except your inverter which probably would have kicked on. If your inverter is still charging, then you need a way to turn the power off to it as well. You never know what "electrician" hooked up things before.
So now that the power is off, go look at the meter. I am sure it is a newer digital one. It will periodically show how many kWh are being used. With everything off at your house, that should be "0.00" . If not, you have friends and neighbors hooked up to your meter.