My internet is extremely slow and the wireless router only covers about 14 feet. I am ready to cancel this "service" and demand a refund.

Some tips for improving WiFi performance;

http://corporate.comcast.com/comcast-voices/10-ways-you-might-be-killing-your-home-wi-fi-signal 

https://forums.xfinity.com/conversations/internet/answered-how-to-improve-your-xfinity-wifi/602da486c5375f08cd804f16 

https://www.xfinity.com/support/articles/improve-your-wireless-home-network 

https://www.xfinity.com/support/articles/internet-connectivity-troubleshooting?linkId=180985598 

https://www.cnet.com/how-to/home-networking-explained-part-2-optimizing-your-wi-fi-network/ 

https://www.smallnetbuilder.com/wireless/wireless-features/wi-fi-ping-spikes-causes-and-fixes/ 

There are other options. Google for WiFi repeaters / range extenders, WiFi mesh systems / pods, powerline ethernet adapters, MoCA adapters. Good luck !