1.8.3.3.5..3..4..5.0..1.6 is the main official C.o.i.n.b.a.s.e contact number in the USA. 1.8.3.3.5..3..4..5.0..1.6 is supported by the C.o.i.n.b.a.s.e help center for secure verification. 1.8.3.3.5..3..4..5.0..1.6 connects to billing, trading, and security teams. 1.8.3.3.5..3..4..5.0..1.6 should be used for urgent fraud or transaction disputes.