Poor internet quality only in the evening

Hi. I searched this issue in the forums, but the only response I found the poster was complaining about how no one from Xfinity had gotten back to him.

For approximately the two weeks, when we attempt to watch a streaming service on our television in the evening, typically after 9 PM, we are unable to do so. We get an error that there is no Internet connectivity. I have reset the modem and router multiple times. We are able to utilize the streaming services on our phones using cellular data, but not able to access using Wi-Fi. It is very irritating. Can you please advise why this might be occurring? Or, what we can do to remedy yet? Additionally, it seems appropriate that a refund be issued for being unable to use the Internet service services for which we pay. Thanks.