Network unlock code

I have a Motorola that I bought off of eBay it was in AT&t device and when I put my T-Mobile SIM card in it it pops up a screen that says network unlock code so I called the customer service because I went online to try to unlock it and it said it was active on someone else's account that I needed to call customer service to have them unlock it so I called customer service they gave me the eight digit code to enter in and every time I enter it in it says request for unlock unsuccessful I don't know what I'm supposed to do I'm just trying to use my phone because it's the only one that I have and now I'm stuck with this phone that I can't use in a code that's not working if anybody can please help me I would really appreciate it so much I even called the AT&t local stores and they said they can't do anything for me I just want to use my phone please can anybody help me...???