Re: Bt hub
If you have a disc are you using a Smarthub 2?. There have been reports of the odd Smarthub 6 losing their Plusnet log in credentials after a firmware update but not a failure to allow a log in. I have found when swapping hubs it is sometimes necessary to close down my browser, which presumably clears the cache and reopen it before trying to access a different hub. Have you tried this or even a different browser?
If this fails have you tried doing a factory reset and setting it up again from scratch?