Comcast Data Delivery

I believe Comcast may be throttling my Internet. On my 500 Mbps plan I am only seeing 5-10 Mbps on both wireless and wired connections. Just a few days ago I got 300 Mbps on my laptop and cell, and 120 on my console. No hardware changes, just slow speeds for two days. I've restarted my modem and router and tightened all my cables, Comcast please explain why my service is so slow today, I am trying to work