Hi, I have a BV8000 PRO, it works fine on both AT&T and T-MOBILE network. So I'm happy to upgrade it to BV9000 PRO, and I just got it today. When I put my old SIM cards on BV9000 PRO, it can't find service on AT&T network. T-Mobile works fine though. I don't know how to return it on TOMTOP, ...