bgsd,
I don't think Brazilian consumer laws are that bad...
Please look at this link:
http://www.idec.org.br/consultas/codigo-de-defesa-do-consumidor/capitulo-iv, "SEÇÃO IV Da Decadência e da Prescrição", article 26. The law grants you a 90 day warranty, independent of the contractual warranty from the vendor. That means it sits on top of Keysight warranty.
Although Daniel still needs to clear why you only have 3 years of contractual warranty, if worlwide it is 5 years, you can check and see if you still have this 90 day valid. The catch may be in this paragraph:
" § 3° Tratando-se de vício oculto, o prazo decadencial inicia-se no momento em que ficar evidenciado o defeito."
A free translation: If this is a hidden defect, the 90 day legal warranty starts to count at the moment the defect was perceived.
I am not a lawyer, so I suggest you talk to one, and with the local Procon on your city.
If all warranty options are now void, Keysight can only charge you if you agreed with the repair terms. If not, they must return you the device in the same condition.
Also, note that the law specifies a maximum 30 day time to effectively repair the device. This is where a lawyer can help you. An interpretation may be that the original repair is not completed yet, as you received a replacement, and this replacement also failed. But again, don't take my word here, seek legal advice.