Upload speed is nonexistent

Hi I could really use some support from an Xfinity employee. I’ve called in many times and have only been told my equipment is the issue and not taken seriously. My upload speed is horrible. It can spike up to fantastic in moments most of the time it will spike and drop between 1.5-50 a second. Huge ranges and never in the same bracket for long. It makes gaming impossible and even something like uploading a photo to facebook takes several minutes at times. 

my plan speed is 300 down and 100up. I get no consistent pin and jitter numbers when I do speed tests it is all over the map. This has been happening for months. At least 6, I replaced my old equipment, ran new coax rg6 cable from the main in line all the way directly to the modem. No splitter or anything else between main feed into home and internet equipment. Even after replacing to the newest rated modem/router it has improved nothing. There is literally nothing else I can replace or improve in my home and every time I call in I’m told it’s my equipment and the tech will need to be in home. I’ve tried to simply request a fix and evaluation of the connection at the poles to the main home as the weather here in Pennsylvania is terrible in winter and the lines are fairly old. Simply put I’m told no. Many reason why but always just a no they’re part of a schedule maintenance and don’t get evaluation for an example of a reason I was given. Right now I can’t use my internet. Download is fine but I can’t rely on this anymore. I really don’t want to cancel service but I’m out of options and get nowhere when I call. I’ve been on the phone with support for over 3 hours in one go before. Many calls aside from that. Please help.