I can't log in to my iCloud account to configure my iPhone 4 after restoring it to factory settings.

I have this weird problem with my old iPhone 4, and it frustrates the **** out of me.

I had some issues with the syncing of my iCloud calendar, and after trying some different things I decided to restore the phone to its factory settings. iTunes said I had to disable Find My iPhone before doing so, so I did.

So after restoring the phone to factory settings it prompted me to log in to my iCloud account, because I had the activation lock activated... But I can't. The phone (and iTunes as well for that matter) says that I entered the wrong Apple ID needed to unlock it. I have no idea why it would say that, because I originally bought the phone myself and I'm sure I never used any other Apple ID to log in. It even says I have to use the Apple ID t*****@gmail.com, which is supposed to be my email address (I don't use any other email address), but clearly something is wrong. And it's not that I'm entering the wrong password either, because I can still use it on my other devices.

So for the past few hours I've been trying all kinds of things, from resetting my Apple ID password, to restoring the phone to factory settings again, ... I'm at the end of my breath now. I need this phone, because well, it's my phone, but I have no idea what to do.

Anyone else ever encountered this problem, of know of a solution? Any ideas would be very appreciated ...