How to unlink iphone serial number on supportprofile.apple.com?

Question

iPhone

Good afternoon! Having recently bought an iphone 5 from a friend and safely unlinked it from a friend’s itunes, I calmly tied it to my itunes id, but trying to link it to my apple id on https://supportprofile.apple.com/ ran into a problem that the serial number could not be tied - writes, already tied to another, going into the profile of a friend - he was not there - and tried to bind s / n to his id - the same result. The phone was bought new through lite-mobile - the phone itself is from the USA, apple technical support did not help in any way - it says that if the s / n is not tied to your id - then we cannot say to which and when it was done, because. information is closed. The friend always used one apple id and did not even know about the existence of https://supportprofile.apple.com/. What can be done in this situation? And what is fraught with that s / n is tied to another id? And is there any way to unbind it?