Unlock code Sony Tablet P

hello
I bought a sony tablet p on ebay.com. I live in Russia and I will only use the tablet with local telecom
operators.

I`d contact AT&T directly at 1-800-335-4685. They said that impossible to give me unlock code for my device.

I had to go through a 3rd party unlocking company to have that done for me. They have no unlock code in their database for Sony Tablet P AT&T contract.

What next to do?

[Edited to comply with Guidelines]