Speed and cost

First. Please try starting here if you wish;

https://forums.xfinity.com/conversations/your-home-network/connection-troubleshooting-tips/602da777c5375f08cdea3db9 

user_bd3adc thank you for using the Xfinity Community Forums to reach out regarding your speeds. I know how important working service is and would be happy to get you up and running with the speeds you anticipate. Firstly, are you having concerns with wired or wireless connections?

@user_bd3adc 

Have you had a chance to see if any of the tips at that link apply ?