I have had this problem three times in the last 18 months or so. I've learned to call my provider, Xfinity/Comcast. Usually, someone is able to reset everything, although the task is grueling for most. For reasons I've yet to figure out, nobody will ever tell me how to access my router settings.
ln the last year I've had nothing but trouble with Roku, usually ending up watching premium channels on my laptop, which is annoying to say the least.
EDIT: It being Thanksgiving and I have a cold or covid or flu, I relearned how to access my router settings and switched them back to b/g/n. (I have no idea why they keep reverting.) If you're a Comcast customer, here's the link for accessing the router (after you log into your account): https://forums.xfinity.com/conversations/internet/answered-how-do-i-log-into-my-xfinity-provided-mod....
A warning: when they say "admin" and "password" they literally mean for you to use those words to log in to router setting. Then, it's going to ask you to create a new password. It is also going to ask you for your old password. Huh? Well, the old password is....."password." Ugh.
