impossible to connect to itunes store

Bougth a new Iphone 5s last week, updated it to iOs 8.3 with itunes on my computer, and tried to configure like a new phone but it does not conect to app store.

All the functiones on the phone work properly, wifi an 4G conections, video playback, icloud, except for the App Store wich doesnt seem to achieve a conection when trying to log in. I can navigate trougth the store and see new actualizations, but when i try to download apps or conect to my apple ID, even on the app store settinge at the settings app, it displays the message "imposible to conect to itunes store". It is not an apple ID probles cause i can log in in every other apple devices i have without any trouble.

I´ve tried restoring the iphone or downgrading the software but it does not work. also changed time configuration. and every restore mode avaible.

can´t log to the store with any other apple ID, and even cant actualize apps installed with itunes.

If any of you have any idea or suggestion before returning the device to the seller, thank you very much.