My Apple ID is broken

Hello there.

I seem to have some unusual behavior associated with my apple id. It appears my apple ID has been split into two, where some services (such as using iTunes to authorize a computer, and iMessage on both iPod Touch and iPhone 4) seem to only recognize the (now forgotten) login details that I first used with my Apple ID, while other services such as the App Store seem to work flawlessly.

You see, about 6 months ago, I changed my Apple ID email address, carrying over my purchases and other things. After that, iMessage broke. I didn't care much for it back then, so I ignored it. Now that I'm setting up my iPod again, I've reset my iPod to factory settings and it is able to access iMessage. The problem though, is that iTunes still has an issue with authorizing my PC, which I must do before resetting my iPhone to factory settings, because there are purchases on my phone that will not sync unless my pc is authorized. Every time I attempt to authorize my PC, I'm asked to login with my old email address autofilled. Whether I login with this email, or my current one, even with the correct password, iTunes says that "The requested resource could not be found."

I don't want to have to go to the apple store to get this fixed, they come up with all these BS fees, like the $33 fee just to call customer support. Does anyone have any way to fix this hiccup in my Apple ID?

Things I have done to attempt to fix this issue:

• Reset all settings (not a factory reset) on my iPhone and iPod Touch. No success
• Factory reset my iPod Touch. Some success
• Fully updated my PC, including operating system updates and iTunes updates. No success.
• Ensured both iOS devices are up-to-date. Due to the ages of the devices, my iPhone is stuck on iOS 7.1.2 and my iPod is stuck on iOS 6.1.6. No success.
• Fully rebooted both devices before attempting to log into iMessage. No success.

I've listed this as an iTunes issue, even though the exact cause of the problem is my Apple ID. Please reply A.S.A.P.