Router, Modem and Xfinity Account compromised

My Netgear router has had its password and security questions changed without permission. The cable modem attached to it has been restricted completely. This is part of a much larger issue (Breaking and Entering, Perverse Threats and so far only one sexual assault).

Anyway on to my question, I found an unknown device on my network and blocked it.
2 days ago I tried to check my bill and I couldn't login. I reset the password and today I logged in to pay my bill and couldn't login again.

Can anyone tell me what I'm supposed to do or at least what kind of IT help I actually need?