Xfinity Assistant not helpful in scheduling appointment

I had a technician come out to my house last week because our internet was slow and insisted I had to get a new modem/router because mine was too slow. I spent $200 and my internet is now slower than before with my previous router/modem. I've been contacting Xfinity assistant multiple times to try and get a technician to come out but each time it says "everything looks fine from our end" and terminates this chat. This is absolutely unacceptable. Not only did an Xfinity representative insist I spend extra money but now I cant even get them to come out and figure out what the problem is.