Slow speed: receiving 150mb on a 1gb circuit

Hi, how can I talk to a support agent about slow internet speeds? 1800xfinity restarted my modem/router twice, no luck. And no way to talk to a live human being.

Hoping to talk to someone in person to troubleshoot. Paying for 1g, receiving no more than 150mb and less than 70mb at other times.

New customer 4 days ago.