Because theft of service is charged as a rate and not a fine, there is no simple path to dispute the penalty. Overturning the charge generally requires proving the DEP’s specific accusation to be untrue, or determining if they have valid proof to charge you. The DEP is also required to send notice of any violation; failure to do so would be grounds to fight an attributed consumption charge. However the process can take a long time and requires constant calls to the DEP, which ultimately often leads to the DEP disregarding your appeals.
You can read more in our article about sending appeals to the DEP.