Nubank is one of the biggest startups in Brazil and I am a Nubank customer and I must say they have the best service available. Treating customers as customers.
The customer support is the best! No waiting, no pre-recorded messages, no muzak, no menu. A real person picks the phone and talks to you. Oh and the app is a delight!
Customer here, as well. IMHO, the best company currently in Brazil.