Down speed supposed to be 500mbps, Receiving 15-25 During download.

For the past two years I have had both the Gigablast (Fiber) and the Ultimate 500 (Normal) and have received disgustingly low speeds during downloads. Just yesterday, I was attempting to download a 28 gb update for Modern Warfare, which shouldn't have taken more than 15-20 minutes. It took FOUR and a half hours. The download speed stayed consistent at 25Mbps, not MBps and would regularly drop to kbps every minute or two. This is 20x slower than what I currently pay for. This device is connected via ethernet on a Gigabit capable line. I have found information about multithreaded connections vs singlethread connections, But I do not believe this to be an issue because I have received 200+ on previous internet plans on the same device. (Which is still not good considering the adv speed). This is not a normal congestion issue, because the speed never bounces up and down. I have never seen the download speed above 100 mbps. Please help. Thanks.