Sue, First, a hearty welcome to TS. Sorry we could not have met under more pleasant circumstances.
I’m really not sure what benefit my experience with Comcast will be, but FWIW:
The service provided has been great, in that I routinely surf at 1.5+ MPS. But the tech support is generally deplorable (though it has gotten better of late).
When I first subscribed to Comcast (about 2 years ago) I had about 3 weeks of absolutely dismal tech support. Fortunately I no longer have to deal with them. And you are right; they think Macs are what’s for lunch.
Around here, Comcast does not do anything per-se. They are like a general contractor with numerous subcontractors, each with a distinct responsibility--cable TV installer, cable TV repair, broadband installer, broadband repair, fix cable from street to home, fix cable from junction box to street, fix cable from hub to junction box, well, you get the idea.
So when there is a fault/problem, another work order is opened and a week later, who ever shows up, blames someone else along the line.
Since you are getting a signal and the service/connect rate degraded over night, I do not believe the problem lies with your computer. If the signal becomes degraded at any point along its path, you connect speed will drop. This may or may not be evident in the quality of your TV signal.
There are, unfortunately, numerous ways the signal can degrade such as power surges and spikes, the line can become damaged or wet, or even someone hacking in to the line and is pirating the signal. The list of things that can go wrong is very long indeed.
Perhaps these suggestions will help:
Since Comcast is a franchised monopoly regulated by our county, the county agency established to oversee Comcast and resolve customer issues is very helpful. Do you have such a thing?
Complain about the TV reception. By boosting that signal, your broadband signal may also improve.
Complain and start working your way up the supervisory chain. Concurrently, contact Comcast’s senior management, describing the situation and what you have experienced. Keep detailed notes.
Notify any agency that oversees Comcast or even has a human interest in your plight, such as the news media in search of a story, or your representative who may be looking for votes.
And, like Kelly said, you need not pay for service you’re not getting.
Harv