iCloud sign-in greyed out on iPhone 4

It all started with changing the email associated with my Apple ID and changing the password at the same time. After wrangling with someone on the phone, I finally got signed out of iCloud in my MacBook Air and signed back in with the right email and password.

But then my iPhone 4S, which HAD been accessing iCloud with the new, correct email, reverted to the old, incorrect email. I managed to sign out of that, and could not sign back in. The "Sign In" was greyed out.

I hadn't yet upgraded to Yosemite, so I took the time to do that and to upgrade the iPhone's software. Everything is shiny, new, and the latest version. MacBook can sign into iCloud. The iPhone cannot. The "Sign In" Is still greyed out.

Went online and researched the problem. Found out that you need to turn on "Restrictions." Did that. "Sign In" is still greyed out.

Please, someone, is there a fix for this? I've wasted a large part of the day that I couldn't really afford to waste on this problem.