Download speeds

I have blast internet and I am getting less than 1/3 the download speed I should be. Contacted customer service, they sent a tech, he was here for more than 3 hours. He got over 900Mbps coming in to the modem but only 44Mbps from the router. He said the router was probably the problem. As a check I connected a different router that I had on hand, still same issue. He then determined that it was probably the modem. I bought the modem 2 days before he showed up and installed it brand new (Arris SB8200). I don't think he was very familiar with this modem as he tried to connect ethernet from one port to his laptop and the other ethernet connection to the router and couldn't figure out why his laptop and modem wouldn't both connect at the same time so he had to keep resetting the modem with only one connected to make it work. This is hoe he determined that my issue was probably the modem and that I should either buy an all in one modem or rent one from xfinity for $17 a month. Only problem is this brand new modem isn't made to work the way he had it connected, the two eternet ports on it are made to basically piggy back both to a router with two eternet inlet ports to boost the signal, you can't run two devices at once. This is how he determined that the brand new modem was the issue. My problem is that I am paying a lot of money for blast Internet and only getting 44Mbps through the router and only 93Mbps through the eternet. The tech was herw, nothing is fixed, and I am still paying a huge premium for blast. What is my next move?