OK, so just to make sure - you went into Manage your Apple ID, and changed your old Apple ID to the one you currently have. But that old ID is still signed onto iCloud. Right?
If that is right, then this is what you need to do:
1. Sign back into Manage your Apple ID and change your Apple ID back to the old ID (this is temporary - do not Verify it - just press Done when it has been changed):
Apple - My Apple ID
2. On your device go to Settings>iCloud, scroll down to the bottom and Delete the iCloud account from your device. Use your current Apple ID password. Don't worry about the warning messages. As long as you have been syncing to iCloud, everything will redownload once you sign back in.
3. Once the iCloud account has been deleted, go back into Manage your Apple ID and change your Apple ID back to the new one (you may need to verify that one again).
4. Go back into your device under Settings>iCloud and sign on with your current ID.
You should be all set!
Cheers,
GB