mismatch between the iPhone serial number label & the software serial number displayed on the screen.

Anybody has this problem where the iphone serial number label and the software serial number does not match? I went to the authorised service center QCD at Singapore and the staff there (by the name of carmen) informed me that they can't give me a one-to-one replacement on the spot even though my handset is still under warranty. My iphone 4s has this wi-fi greyed out problem, that is why i went down to the service center. I find it very strange and demand an explanation. However the manager there (desmond) told me that they can't do the exchange nor comment on why this problem. They have to wait for apple's instruction

Could the phone been tampered with at the factory level? or apple store sold me a refurbished set that had been tampered with? I had never send the phone for any repair at all nor open up the phone before