I would start with PEPCO, but if they don't immediately repair, you should probably have a lawyer send letters to Pepco, your neighbor, and their contractor advising them that their work has interfered with your property and you expect them to repair it ASAP. Unfortunately, you could get caught in a circular game of blame. FWIW, Pepco and the other local utilities seems to be more responsive these days given their regulatory scrutiny. Also, can't hurt to call your council member's office if you run into problems, thay have ways of applying pressure to assuage angry constituents.

My neighbor is having some home renovations done. In the process of renovating, PEPCO was working on their property and cut one of our lines (sewer), resulting in repair work. Who is responsible for paying for the repair?