C6300 slow, less than 10 Mbps. Help!

I am a Spectrum (formerly Time Warner Cable) customer. My internet speed is very slow (1-3 Mbps), both with WiFi and when I plug my laptop into one of the Ethernet ports. I should be getting at least 17.5 Mbps. I unplugged it and plugged it back in several times, doesn't improve it at all. I also changed the SSID from the default NETGEAR67 to something unique. A technician from Spectrum inspected my incoming cable connection said everything looked good. At this point I don't know what else do. Help!