faster internet speed

I currently have an XB7T modem connected directly to my computer but my download speed, 418mgps is well below the speed allowed by my plan, 1100mgps.  Conversely my upload speed is fine, 39.8mgps.    I live in Richmond, CA, an East Bay suburb of San Francisco but for some reason my Xfinity host is located in San Jose.  What do you recommend I do to correct this situation?  Does Xfinity have a tech support number within the U.S. I can call to rectify this situation?  It takes forever to call their customer service line and even if you do, you never get a live human being to answer the phone.