Why can't the AT&T model BlackBerry phones be serviced outside the U.S?

I bought a Blackberry Cellphone TORCH 2 9810 AT&T means that its from U.S but i live in INDIA . I have faced many problems like i cant access blackberry world or youtube or facebook . i cant even download any apps . i cant even get to know my location since the gps is not working . IN SHORT ALL NET RELATED PROBLEMS ARE OCCURING. also there was some issue with the speaker bt it carried away. WHen i visited the blackberry expert center they told that since its an AT&T mobile so they donot have the authority to repair the phone.

Are you sure it's unlocked? If BlackBerry service center won't fix it (which is not cool) then is there a cellphone repair place you can go to?