i used to be with sprint. now i am with at&t i had my sprint phone unlocked. My phone is a samgung galaxy s7. it was working fine until i did a system update and now it won't let me make or receive calls and text and mobile data is not working. i have at&t sim card in the phone and i get a message saying "Invalid SIM card". what can i do to get my phone working?
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Please I have problem upgrading my phone, its an international phone (USA) but i'm based in Nigeria... i called samsung and they refer me to my carrier... bcus the phone is locked and to unlock it i have to travel to the U.S to do that, pls is there no other way this can be done? all i want is to upgrade from 6.0 to 7.0 i have tried all i can. please i need assistance.