Can't sync with USB - Why do I HAVE to use iCloud?

Just got an iPhone 6. Won't sync the Calendar using USB. Error '... because the calendar is in use by the iPhone'. The support geniuses say I have to use iCloud. Well... not according to this article that's less than two months old: Sync your iPhone, iPad, and iPod with iTunes using USB - Apple Support

Everything is the latest version. It syncs everything else, but I get the error and the month view of calendar on the phone shows days with events, but tapping the day doesn't show any events for that day.

They won't admit what the problem is, just that I have to use iCloud.

I'm returning the phone, already have the return shipping label.