Carrier cannot unlock iphone 4
My carrier T-Mobile UK cannot unlock my iphone 4. They have sent the request to apple who have replied that it cannot be done, but with no further details. The handset is my own and I have reached the end of my contract with the carrier and wish to switch. The only advice T-mobile can give me is to contact Apple, but from the Apple website they direct me to my carrier for unlocking. Has anyone else experienced this issue?
iPhone 4, iOS 6.1.3