I would go the Amex route as well. You should be netting in the 180s to answer your question. The Amex office is just below the Cortes building in-between Sol and Paseo del Prado (Plaza de las Cortes, 2). They're open from 9:00-17:30, M-F; 8:00-12:00 on Saturday.
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Ongi etorri!