Frequent Intermittent internet drops since switching to NOW internet

I have been using NOW internet for about 3 weeks and my internet service goes out every day and sometimes multiple times in a day. When I first got it, it was difficult to get it working but with the help of online tech support, it started working. The very next day, the internet went out and would not recover even after several power recycles. Tech support scheduled a tech to come out. But because I never had any problems with my old modem, I thought it must be the modem, so I took it up to the local store thinking I could just swap it out for a new one, but they said they were not allowed to do that. 

So I took it home and reconnected it so the tech could test it when he came out. After reconnecting it, it suddenly started working. I received a text from xfinity saying "We fixed the issue impacting xfinity internet in your area." This after telling me several times earlier in the day that there were no outages in my area. I don't know if they saw that my modem was back online and that is what generated the message or if they really fixed something. 

Since then, the internet has dropped multiple times, sometimes for a few minutes, sometimes for a couple of hours. After the first issue, I thought that maybe if I disconnected it for an hour or two, like when I tried to get it replaced, that that would fix it. Lately, it seems to come back without even unplugging it. 

I am also having severe problems using my phone over wifi with calls dropping every minute or two, to the point yesterday where I had to turn wifi off on my phone in order to complete any phone calls. 

This is the worst internet experience I have ever had. Either the modem/router I have that was supplied for use with NOW is defective, or it is garbage. Is it possible to get a new one shipped to me so I can see if it is just the modem? I don't know what else it could be because I never had this problem when I used my own modem and router. I have tried using the NOW supplied modem alone, and I now have it set for bridge mode to use with my Synology router. The problem seems to be the modem functionality.