O to official Mi service center and tell them the problem.Well Amazon replacement/return policy is of 10 days and I doubt they now do accept mobile phones return or replacement.Should have went to service center during first 10 days and get a DoA(Defect on Arrival) from them.With DoA I think they might have replaced ur phone in that 10 day period.Now it is too late bro.But visit service center once and see what happens.Yes. Redmi Note 3 do support 64gb SD card.