If you can’t log in to to your Twitch account on other devices, that’s not an issue this 3rd party developer community can help you with and you’ll need to contact Twitch support https://help.twitch.tv/s/contactsupport
As for removing followers without blocking them, no, there’s no dedicated endpoint to do that because there’s rarely a legitimate reason to make a person unfollow that you don’t also want to block. What would be your use case for needing to remove followers but not block them?