Just because the same word exists in both Spanish and Portuguese doesn’t mean it’s the best word to use or that it’s one that Brazilians normally use. There are many examples of words used more or less frequently in one language or the other. Responder and contestar help illustrate this point.
In Spanish, when answering a question or responding to someone, the most common verb used is contestar. However in Portuguese, the verb responder is used most frequently.
English: He asked me a question, and I answered.
Spanish: Me hizo una pregunta, y contesté.
Portuguese: Ele me fez uma pergunta e eu respondi.
Sound Brazilian! When you answer the phone in Brazil, say Alô! but when you talked about answering the phone use atender, not responder.
English: My friend called during my flight and I couldn’t take his call.
Spanish: Mi amigo me llamó durante el vuelo y no pude contestar.
Portuguese: O meu amigo me telefonou durante o voo e eu não pude atender.