I Have an off contract Note 3, I want to use on AT&T. This device is an old phone, currently inactive. It is network locked. I took it to AT&T got a SIM card, but it will not connect. They said take it to Verizon for unlocking. I took it to two Verizon stores, one claimed it was illegal to do it, the other said they're not responsibility for this type of work. This is my phone bought and paid for, and not under any contract. How do I unlock it?