It's the same issue that many of us are having. Anyone else using the connection for streaming video will cause frequent and regular ping spikes. It's been happening to me since around the beginning of the year. Nothing I've tried has fixed it, so I'll simply be changing ISP's.
Buy your own router. Isp routers are not very good, they're pretty sufficient for web browsing etc but for online gaming you really need to invest in a good router. Isp routers are free for a reason.