Internet dropping constantly

For over a month now, my internet has been lag spiking or disconnecting. I play video games at home and as a result, I've had to stop playing online games because I would disconnect or lag. My girlfriend works from home and would constantly disconnect from meetings. I've called comcast numerous times but have yet to get a solution. Here's what we've tried so far
-Restarting the modem
-Upgrading our speed from 50 to 250

-Updating our modems firmware

-Replacing Coaxial cable 

-Updating speed from 250 to 500 (because for whatever reason you can only have 8 devices connected at one time)

-Dropping our devices in our household down to 8

-Upgrading to a comcast modem

-Getting new lines dug outside

-Ran virus scans on all of our computers

We've had a technician come out, but that didn't solve the problem. Our computers are all plugged in via ethernet cords. Is there anything else we can do? I'm really stressed out