iPhone 6S plus got activation locked to some different / unknown icloud id. f*****@yahoo.com

My Story:

I have official Invoice, the iPhone was unboxed by me personally on Feb 2016. Since then I was using my iPhone normally updating to its latest iOS releases. The Warranty was activated on same date, it was unboxed.

This iPhone is used under single iCloud id which never has been changed. No family member uses this phone, its all used under my personal iCloud ID. No Family Sharing. I have never Jailbroken this phone or Never Installed any Third Party Developer Apps till date.

What Happened,

The phone is running iOS 9.3.5

Today, Backed up my iPhone to Computer.

Went to 'Settings' -> 'General' -> 'Reset and Erase all settings'

The Phone asked me for my Passcode,

then for Restrictions Passcode,

Finally, I was asked to enter the password of my icloud id, to turn off 'Find my iPhone' before resetting the iPhone.

I also received an Email on my apple ID that my Find my iPhone has been turned off on this iPhone.

As the phone was done with Factory Reset part, the third page of 'Setting up your iPhone' asked me to Enter iCloud Password for the user id which was never associated to my iphone since the day I unboxed it.

This is super strange Issue. I tried to login with my iCloud id, which didn't worked Shockingly.

Then I called up Apple Care India, immediately. They said, their Tools are down for few hours, as Apple is upgrading their systems. Hence, I had no option to wait all day until evening.

I called them up. They have raised a Issue. Even the Supervisor on call was shocked hearing this Issue.

They took my Invoice Sales Receipt of this iPhone.

Now, I have a waiting time of about 4 working to get reply from Apple Team India.