Internet Problem in New Place

So, I had eatel come out and set up cable and Internet for a good price. However, the jack that he installed the modem/router on is upstairs. I was worried about the wifi strength and asked him about it. He insured that those routers work in a downward cone. Well it's been a week and I'm trying to play some PS4 online and it lags on and off, sometimes it's fine others it kicks me. Netflix also won't load movies at times. What are my options here? I know I can run a hardwire to my PS4 but my TV and PS4 are mounted on a fireplace wall. There is a coxial jack downstairs, can I run my router off that Jack?