Roku not working after modem switch

Hi,

I just switched to a new modem last night (from the Comcast modem to my own). Everything works on my roku except the xfinity streaming app. I know lots of people have had this issue.  Serial numbers match what's listed on my account. Customer service has been no help.

ComcastElla, if you're still online, it seems like you've had lots of success.

Please help!

Thanks