iMessage: Waiting for Activation (iPhone 6)

iMessage was operating perfectly on my iPhone 6 with iOS 8.3. My Windows version of iTunes made everything go weird on my phone, so I ran a restore on my home iMac.

Ever since then, about 2 weeks ago, iMessage has refused to activate, have the error "Activation Unsuccessful". I can only use my iCloud account mail address.

I have run a restore twice since then, including this week with iOS 8.4.

I have used different methods of switching iMessage on and off, signing out and in with iCloud account (using only wifi, doing a hard reboot, using only mobile, etc).

I seem to have run out of options and ideas.

Anybody out there that knows how to sort out this issue? PLEASE