Unlock a device

Hi, I've been trying to unlock an iPhone 6+ for the past month or so, I've submitted the request 3 times and each time it's been denied. I went to an AT&T store and spoke to an employee who submitted the request for me for the fourth time and it was still denied. I've contacted the customer service line and spoke to a woman who told me my request should be approved this time because it was approved by a manager already, when I received the email a few days later it said request denied.The emails all say the request wasn't approved because the account holder info doesn't match their records which I don't understand because the man from the store didn't mention that nor did the customer service woman. I already paid the whole phone off and it's not connected, I'd like to be able to unlock it because my mother is in need of a phone and this is truly frustrating. Help.