Slow Gigabit Internet

I just recently upgraded my router and internet with Xfinity to 1 gigabit. I am getting incredibly low download speeds....often less than 20 mbps...what is going on???? I am supposed to have blazing fast speed. I work from home and I am on video calls all day. I cannot count the number of calls that I've had to abort and switch to a voice call on my cell phone. I am EXTREMELY frustrated and ready to throw out Xfinity/Comcast for good!!! Help!!!!

Tony Norkaitis