Incredibly slow speeds - Fed up with lack of support

I have the Gigabit plan and I'm using my own Docsis 3.1 (Arris T25) modem. A month ago, I started noticing speeds in the 80-120 mbps and a tech came out. That day miraculously it was up to like 500 mbps, still not what I'm paying for but better. Fast forward to about 2 weeks ago. I'm sitting on speeds in the 15-20 mbps range.  A tech came out told me it was the line from the node to my house looked good and that he was seeing the same speeds as mine. That there was probably just someone with a bad connection on the node severely slowing me down. He'd put in a ticket and it'd be fixed within a day or two. Well now, all this time later, still not fixed and it's even slower. I called tech support again and A) they can't even see where he put a ticket in to have someone fix the node B) all they kept saying was you need a Comcast modem (BS.... It worked fine before). ANOTHER tech is coming out in a few days but I can definitely see this getting worse. NOBODY seems to be able to fix it. 

Wish there was something I could miraculously do to make my internet speeds better and not have to deal with Comcast. If there was ANY alternative at all... I'd drop Comcast in a heartbeat. It's ridiculous to me that they continue to make me pay for a product that I'm receiving 1/10 of what I pay for without any urgency to fix it. 

Any ideas on what to do would be appreciated. Or better yet if someone from Comcast is listening... PLEASE HELP.