How to legally get our landlord to cough up the $?

Our electricity bills skyrocketed when the 2nd floor apartment was rented out. The bills tripled and quad a few months since then. The 2nd floor tennants were not asked to put the electrical in their name. The landlord is charging them random amounts for electricity in CASH every month & they were never shown a bill. We are almost certain that he has been scamming us by having us pay for their electricity while he collects the cash. After we do the loop check to see what sources we are providing the electricity to is there a way to take legal action agains him? Any lawyers or other tennants out there know if it would be worth it to follow up w/this in the court system?