Slow internet speed

I have been a xfinity/comcast customer for decades. I started moving in to my new home. Went to the xfinity store and signed up for service at my new home but keep my old service for a month or so. Installer had to run all new cable from the pole to the house then inside. He set up everything all the way to the gateway. Said it was working fine and left. Two days later I returned to my new home. Hooked up my computer via a ethernet cable. I ran a speed test to make sure everything worked right. I signed up for the two gig speed, results were 932 mbps. I worked with the xfinity bot for almost 2 hours with no results. Then I called their customer service and after an hour and half she said the gateway was bad. I went to the xfinity and exchanged the gateway. returned home and hooked it up.. After booted it up and yes the speed was changed, now only 543 mbps. I tried the xfinity app on my phone to register the gateway. Got to the part where you have to scan the qr code and the app said I need to call customer support. I called the tech support an got a guy and I quote "this is like a walk in the park for me" I didn't think he meant Yellowstone. After four hours I hung up on the clown. My supper was getting cold. only thing that came out was the speed was back up to 930 mbps. Seven hours later I'm at the same place. Two days of tech support and my time wasted.