Intermittent internet at best

This has been an ongoing problem for years.  Every summer, particuarlly during peak hours, the internet go down, a couple minutes later it would come back and repeat over and over again.  The internet would work for anywhere from two minutes to an hour at a time and then would drop out for anywhere from two minutes to an hour.  Once summer ended typically the problem would resolve.

This year however it hasn't and if anything it has been getting worse.  I have had two service calls (including a supervisor) come out to test the lines.  The first one said everything was fine and left (the problem reoccured within an hour after he left) the second guy told me it was my modem or router.  I just got a brand new modem/router combo (the third modem or router which I have bought, all off their own approved list) and same thing, spotty internet at best.

Just got off yet another chat with tech support (I can practically quote their troubleshooting script at this point) who said I need another tech support guy to come out which I refused because I'm not paying for yet another pointless tech support call.

My suspision is it has something to do on Comcast's end with throttling or whatever it's called because the time it worked the best recently is at the very beginning of the pandemic when Comcast made a big deal about "being there" for everyone working/going to school from home but that quickly went back to the baseline (ie not working).

Does anyone have any ideas of anything I could try or any way I could convince Comcast to take this issue seriously?