Poor WiFi Connectivity and almost no Ethernet connection

I have had Comcast modem for years without a problem (the older model) then all of a sudden it seemed to have reduced Wi-Fi coverage and almost not ethernet connection. At the first tech service visit they tested the signals, and all seemed fine from e test standpoint, so they replaced our old model with a new one. No improvements and now it even seemed worse. So, we had another comcast tech come out and this time they replaced the new model modem with the older version again saying that the older one was better they also removed a coaxial splitter and ordered an upgraded Coaxial cable from the street to my house (since it was 11 years old and apparently an older version of cable). Before the tech lever he tested the signals, and all seemed fine. But quickly it was apparent that nothing had improved, and it now seemed even worse, we could barely get Wi-Fi to stay connected at all. So, we waited for the new Coaxial cable to be installed thinking that that was the problem, but that did not help anything neither. So, I replaced the new old model with another now older model from the Comcast store thinking that maybe I just got a bad modem. This still did not make a difference.

in the meantime, I have tried multiple things at home to try to isolate what the problem may be, I removed all switches in the network and connected direct to the modem but no improvement. I No improved Wifi signal even right next to the modem. Tried resetting everything of course multiple times, tried now Coaxial cables note Ethernet cables noting seems to work.

So I called for another tech to come out (apparently this one was there senior tech), he replaced the new old model of modem again for a new version saying that this is the only way I would get the full upload and download speeds for my service level. Tech again tested signal strengths, and all seemed fine. At first things seemed betters WiFi seemed to connect to a few more devices. But we quickly learned that almost nothing worked with Ethernet. And I had to disconnect most devices from ethernet to get them to work via WiFi, and WiFi is slow and spotty.

That brings us to today, were I am considering buying a non-Comcast model to see if that will work.

What else can I do, the comcast techs do not seem to be able to fix anything and even contradict each other.