Not Receiving Advertised Internet Speeds

I don't know why you're purposely slowing my internet,  We've had this problem for years, and nothing ever gets done until I file a complaint with the FCC. It generally gets cleared up for a while, at least until winter. I pay for a gig but only get about 412mbps. I used to get over 700mbps, but when we use the service a lot, the speed starts slowing. I also want to say we are paying for unlimited service, not the one reg 1

TB service, but the extra 30.00 for unlimited. The service was so bad today that I couldn't even load a web page. Xfinity customer support didn't help. They reset the modem twice but never called me back as promised. Please fix the problem or only charge for the 500mbps per month because you're not providing the promised gig for 106.00 plus the monthly fee we are paying. I also filed an FCC complaint, so I hope to hear from someone about this issue.