Wow, sorry about that experience with their tech support. I personally have a Roku that I love but have never needed to contact support. I hope that's atypical for them because the company seems to produce good products with quite a bit of polish. Sounds like they may have outsourced their support unfortunately.
In your last post, you said "I have Comcast XFinity and connect through Linksys."
This gives you some things to try. First, is there a reason that you are using a Linksys router behind the XFinity router that Comcast provided? If you are very network savvy, and understand how to eliminate a double NAT configuration with these devices, then that's fine. If however, you have no idea what I mean by double NAT, then I would recommend actually removing the Linksys router from your home network altogether and instead using the WiFi provided by your Comcast provided Xfinity router for connecting all of your household devices to the Internet.
Your Xfinity router likely has a WiFi network name and passphrase on a label on the device. On your Roku, try going to the WiFi network settings and looking for the Xfinity network name in the lsit of available networks. If there, join that network using the passphrase listed on the Xfinity router. If you are able to join that network, then see if the Roku works. If it does, then you should likely also join your Mac and any other devices directly to the same Xfinity WiFi network and then power off and disconnect the Linksys from your home network.