Unacceptable Internet Performance whilst Gaming (League of Legends)

I have recently downgraded from Premiere service to Preferred.

With that said, I have begun to experience some major lag spikes in my online games, most notably League of Legends.  This game functioned flawlessly for months while on Premiere.  The speed isn't the problem; I will be able to control my character just fine for most of the game, but frequently throughout the course of the game i experience lag spiking from <50ms to straight up thousands.  This is **, and it is unacceptable.  This is not caused by a problem on my end, I play games all day erryday and nothing about my computer or the connection has changed, with the sole exception of the service downgrade.  the claimed 12-18Mega BITS per second D/L and "up to 3" Mega BITS per second U/L are MORE THAN ENOUGH FOR THIS GAME TO RUN PERFECTLY.  So, what the *** are you guys doing that is causing this problem?

If you think you can dismiss this without truly resolving the issue, you will be disappointed.  I am unemployed and have all the time in the world to pursue it.

In before CAPTAIN OBVIOUS: I do NOT have any viruses, spyware, malware, DRM, AIDS, or other computer infections.  I keep my PC CLEAN AND FRESH.

If the speed downgrade were the cause of the problem, it would be a consistently slower connection.  What I am experiencing is random extreme spikes wherein I might receive data but not be able to send it (can't control character but watch others around me continue normally) or I am able to do neither (in which case my character starts acting like he is having a seizure and starts teleporting around the map).