Hi - same problem for me. Can log into website fine (cleary as I'm able to contribute to this post) put same username and password gets the error message 'You entered an incorrect username or password.' Its been like this for months now!
My app was in demo only after successfully using it for years.I am in middle of problem regarding erroneous transfer of my gas supply so I really needed to see what is happening as they have since added an estimated gas bill to my electric and telling me I am on dual fuel without my consent.I am at my wits end to be honest .Anyway I downloaded new app and it asking me for account no but then telling me I already have this account no but won’t let me log in !
Sorry for rant but this has been going on since April
Changing to a simplier email address (gmail) solved the issue. I suspected that this would be the case but it took me a while to actually get round to it. Now I'm in the app I'm pretty underwhelmed - I thought Id be able to see daily and hourly usage at least.