This is extremely difficult for me to debug, since I can’t just pretend to be you. I don’t have your username or password for Battle.net, so when things go wrong in this process, it’s very hard for me to even tell why.
What region are you in, e.g., EU, NA, etc.? Note that the CN region is not supported, since Blizzard took the Battle.net API down for CN months ago and has yet to bring it back up.