Issues/slow speeds with both wired and wireless connection after Comcast interference

Hey all, not good with all of this but i'll try to give you all the information possible. After years of slow speeds with old equipment, we bought a new router/modem about 4 months ago and set it all up without problem. Our ISP is comcast and they were fine with getting everything set up, our internet speeds increased twenty fold and haven't had an issue since. Fast forward to yesterday, I open internet explorer on my parents computer and was greeted with a message from Comcast telling us they shut our service down during a "quality service check". They wrote that they required information about our connected devices and provided a toll free number. (I did some digging and read that these general are directed towards the modem, which is less than a year old and we were told was compatible).

We called the number and the guy was fine, asked us various information about the modem like model and serial number, and mentioned something about adding it into the system as a compatible unit. When asked why they would shut us down he provided little information and just said they routinely check how the equipment hooked up is performing etc. and this was a routine thing. Whatever, fine, I can only get comcast in my area so they can do what they want.

The PROBLEM arises the day after. He switched everything on for us and we were able to access the internet, but now I have trouble even simply streaming a source video from Twitch, whether it's on a wired connection, 5.0ghz, or 2.4ghz. I usually set up my PS4 with Overwatch over the ethernet, and hook my computer up to the 5.0ghz, and I'm able to stream twitch on source quality and get less than 40 ping on Overwatch, not to mention the other people on the connection. I've been doing this since we set up the new equipment. Now when I try that, the stream is literally unplayable and my ping shoots up to 190+. And like I said, if I try to watch a source twitch stream alone, it lags even though that is the ONLY data being streamed over any device on the entire connection. I've tried every combination of connections, putting the ethernet on my desktop, putting it on the 2.4ghz, etc. Nothing changed the ping/speeds. Ive never had an issue of me streaming something on my computer and affecting another device on an ethernet.

I've tried resetting every device, I've unplugged router and modem, turned them off, reset them. I havent updated any firmware yet but I can't imagine that's the issue, could it? Any insight will be helpful, sorry if this is a stupid question or answered somewhere else, I just have no idea what happened.