VERY POOR ETHERNET CONNECTION

Hoping I can find some guidance here instead of directly for xfinity as I am starting to feel I am being played..I was recently upgrading to the 600mb speed however, I cannot even get 150mbs connected through Ethernet. I have spent days researching all problems with my laptop and nothing. It is not on my end yet, xfinity claims it is. I had the 200mbs plan then everyone got an extra 100 mbs which brings the speed to 300mbs once I upgraded my old modem I discovered I was not even close to getting the speed. I was sent the new xb7 modem (white one) still, no difference in speed and I tried another laptop and the speed is the same a neighbor plugges his laptop into my Ethernet and guess? still slow as [EDIT].  xfinity claimed it was my pc, I switched the Ethernet cable to a cat8, moved the modem closer and higher up and still the Ethernet is slow as [EDIT]. wifi on my iphone and ipad is getting around 450 - 520 mbs which is good, but my pc only has 2 GHz (ordered a new dual band with 5 GHz), but I need the wired speed of 500 or better not wifi. Anyone have any ideas? tech is coming out Friday Dec. 3. Again, nothing is wrong with my laptop, Bios updated, drivers updated, new coaxial cable, new Ethernet cable as well.

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