I cannot connect to the account ingame. I enter my details and it keeps loading. Has anyone encountered the issue?
Same 
just stuck on “Logging in to Activision Account” …
Same thing happened to me, but selecting Forgot Password at the login screen and following the prompts to reset your Activision password fixed it for me.
Turns out when you select create an Activision account using your Battle.net account, the Activision password requirements might reject the password that you use for Battle.net. If this happens, it will just hang on that “Logging in to Activision account” screen and never tell you that there is a problem. So, you need to reset the password to one that Activision will allow to get past that screen.
Hope that helps.