Why is that every fine on cox's end but terribly bad inconsistent on my end for internet speeds?

HI. I signed up for the gigablast in august of 2021 i believe and Ive had issues with it. We switched modems many techs came out etc. My speed at its peak even when it early mornings on a weekday is no more than 600mb download and 4 to 18 upload and that's hardwired...wireless its 96 to 260mbs download and 2 to 15mbs upload. its always inconsistent and its always that low for the gigablast internet plan. why is that? 

been this way remember since 2021 and its now November of 2022.....modem not obstructed...and when tech tests speeds on his devices he gets the max..tech witness on my 4 devices the slow speeds...what to do now?