Received a voicemail stating that my Comcast internet account required urgent attention and to call back at 856 324 3025. I called Comcast's actual 800 number listed on my statement (which has always been paid on time) and the representative noted that in their phone records, no one has contacted me and that nothing is wrong with my account.

I had the same problem.  After an hour on the phone with Comcast reps, mostly hearing "we don't have that number" someone found that this was an actual number in their online security department, but it was outbound only and even though they leave this number, you can't actually call them back on it.  And this is a "communication" company.  wow.  and then the rep wants to know if I want to use their phone service.